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HOME  UNIVERSITY  LIBRARY 
OF  MODERN  KNOWLEDGE 

No.  68 

Editors : 

HERBERT    FISHER,  M.A.,  F.B.A. 
Prof.   GILBERT   MURRAY,   Litt.D., 

LL.D.,  F.B.A. 
Prof.  J.  ARTHUR    THOMSON,  M.A. 
Prop.  WILLIAM   T.  BREWSTER,  M.A. 


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SCIENCE 

Already  Published 


ANTHROPOLOGY      By  R.  R.  Marett 

AN    INTRODUCTION    TO 

SCIENCE By  J.  Arthur  Thomson 

EVOLUTION By  j.  Arthur  Thomson  and 

Patrick  Geodes 

THE  ANIMAL  WORLD By  F.  W.  Gamble 

INTRODUCTION     TO      MATHE- 
MATICS      By  A.  N.  Whitehead 

ASTRONOMY By  A.  R.  Hinks 

PSYCHICAL  RESEARCH   ....  By  W.  F.  Barrett 
THE    EVOLUTION   OF   PLANTS  By  D.  H.  Scott 
CRIME   AND   INSANITY  .    .    .    .   By  C.  A.  Mercier 
MATTER  AND   ENERGY  ....   By  F.  Soddy 

PSYCHOLOGY By  W.  McDougall 

PRINCIPLES    OF    PHYSIOLOGY  By  J.  G.  McKendrick 
THE   MAKING  OF  THE  EARTH  By  J.  W.  Gregory 

ELECTRICITY By  Gisbert  Kapp 

MAN:     A    HISTORY     OF    THE 

HUMAN  BODY By  A. Keith 

THE     ORIGIN     AND     NATURE      OF   LIFE 

By  Benjamin  Moore 


Future  Issues 


THE  CARE  OF  CHILDREN   ...  By  R.  A.  Benson,  M.D. 

DISEASE By  W.  T.  Councilman 

PLANT  UFE By  J.  B.  Farmer 

NERVES By  D.  F.  Harris 

A  STUDY   OF  SEX By  J.  Arthur  Thomson 

THE   MINERAL  WORLD  ....   By  Sir  T.  H.  Holland 


DISEASE 
AND  ITS   CAUSES 


BY 

W.  T.  COUNCILMAN,  A.M.,  M.D.,LL.D. 

Professor  of  Pathology,  Harvard  Uni'versity 


NEW   YORK 

HENRY   HOLT   AND    COMPANY 

LONDON 

WILLIAMS   AND   NORGATE 


Copyright,  191 }, 


HENRY   HOLT  AND   COMPANY 


THE   UNIVERSITY   PRESS,   CAMBRIDGE,    U.S.A. 


PREFACE 

In  this  little  volume  the  author  has  endeavored 
to  portray  disease  as  life  under  conditions  which 
differ  from  the  usual.  Life  embraces  much  that  is 
unknown  and  in  so  far  as  disease  is  a  condition  of 
living  things  it  too  presents  many  problems  which 
are  insoluble  with  our  present  knowledge.  Fifty 
years  ago  the  extent  of  the  unknown,  and  at  that 
time  insoluble  questions  of  disease,  was  much 
greater  than  at  present,  and  the  problems  now  are 
in  many  ways  different  from  those  in  the  past. 
No  attempt  has  been  made  to  simplify  the  subject 
by  the  presentation  of  theories  as  facts. 

The  limitation  as  to  space  has  prevented  as  full 
a  consideration  of  the  subject  as  would  be  de- 
sirable for  clearness,  but  a  fair  division  into  the 
general  and  concrete  phases  of  disease  has  been 
attempted.  Necessarily  most  attention  has  been 
given  to  the  infectious  diseases  and  their  causes. 
This  not  only  because  these  diseases  are  the  most 
impoi-tant  but  they  are  also  the  best  known  and 
give  the  simplest  illustrations.  The  space  given 
to  the  infectious  diseases  has  allowed  a  merely 
cursory  description   of  the  organic  diseases  and 


215143 


iv  PREFACE 

such  subjects  as  insanity  and  heredity.  Of  the 
organic  diseases  most  space  has  been  devoted  to 
disease  of  the  heart.  There  is  slight  consideration 
of  the  environment  and  social  conditions  as  causes 
of  disease. 

Very  few  authors  are  mentioned  in  the  text  and 
no  bibliography  is  given.  There  is  lack  of  litera- 
ture dealing  with  the  general  aspects  of  disease ; 
tlie  book  moreover  is  not  written  for  physicians, 
and  the  list  of  investigators  from  whose  work  the 
knowledge  of  disease  has  been  derived  would  be 
too  long  to  cite. 

It  has  been  assumed  that  the  reader  lias  some 
familiarity  with  elementary  anatomy  and  physi- 
ology, and  these  subjects  have  been  considered 
only  as  much  as  is  necessary  to  set  the  scene  for 
the  drama.  I  am  indebted  to  my  friend,  Mr. 
W.  R.  Thayer,  for  patiently  enduring  the  reading 
of  the  manuscript  and  for  many  suggestions  as  to 
phrasing. 


CONTENTS 


CHAPTER  I 

Paob 

Definition  of  Disease.  —  Chabactebistics  of  Living  Matter. 

—  Cells  as  the  Living  Units.  —  Amceba  as  Type  of  a  Unicellular 
Animal.  —  The  Relation  of  Living  Matter  to  Environment.  — 
Capacity  of  Adaptation  to  Environment  shown  by  Living  Matter. 

—  Individuality  of  Living  Matter.  —  The  Causes  of  Disease 
Extrinsic.  —  The  Relation  of  the  Human  Body  to  the  Environ- 
ment.— The  Surfaces  of  the  Body.  — The  Increase  of  Surface 
BY  Gland  Formation.  —  The  Real  Interior  of  the  Body  repre- 
sented BY  THE  Various  Structures  placed  between  the  Surfaces. 

—  The  Fluids  of  the  Body.  —  The  Nervous  System.  —  The  Heart 
AND  Blood-vessels.  —  The  Cells  of  the  Blood.  —  The  Ductless 
Glands 9 


CHAPTER  II 

No  Sharp  Line  of  Demarkation  between  Health  and  Dis- 
ease.—  The  Functional  Nutritive  and  Formative  Activities 
OF  Cells.  —  Destruction  and  Repair  Constant  Processes  in 
Living  Matter.  —  Injuries  to  the  Body.  —  The  Effect  of  Heat. 

—  The  Action  of  Poisons.  —  The  Lesions  of  Disease.  —  Repair. 

—  The  Laws  governing  Repair.  —  Relation  of  Repair  to  Com- 
plexity OF  Structure  and  Age.  —  The  Reserve  Force  of  the 
Body.  —  Compensatory  Processes  in  the  Body.  —  Old  Age.  — 
Tub  Diminution  of  Resistance  to  the  Effects  of  the  Environ- 
ment a  Prominent  Factor  in  Old  Age.  —  Death.  —  How  brought 
about.  — ■  Changes  in  the  Body  after  Death.  —  The  Recognition 

OP  Death 40 


CHAPTER  in 

The  Growth  of  the  Body.  —  Growth  More  Rapid  in  Em- 
bryonic Period.  — The  Coordination  and  Regulation  of  Growth. 
—  Tumors. —-The  Growth  of  Tumors  compared  with  Normal 
Growth.  —  Size,  Shape  and  Structure  of  Tumors.  —  The 
Growth  Capacity  of  Tumors  as  shown  by  the  Inoculation  of 
Tumors  of  Mice.  —  Benign  and  Malignant  Tumors.  —  Effect  op 
Inheritance.  —  Abe  Tumors  becoming  more  Frequent?  —  The 
Effect  produced  by  a  Tumor  on  the  Individual  who  bears  It.  — 
Relation  of  Tumors  to  Age  and  Sex.  —  Theories  as  to  the 


vi  CONTENTS 

Page 
CAnsE  OF  TuMOBS.  —  The  Parasitic  Theory.  —  The  TRAtrMATic 
Theory. — The  Embryonic  Theory. — The  Importance  of  the 
Eablt  Recognition  and  Removal  of  Tumors 62 


CHAPTER  IV 

The  Reactions  of  the  Tissues  of  the  Body  to  Injuries.  — 
Inflammation.  —  The  Changes  in  the  Budod  in  This.  —  The  Emi- 
gration of  the  Corpuscles  of  the  Blood.  —  The  Evident 
Changes  in  the  Injured  Part  and  the  Manner  in  which  these 
are  produced.  —  Hh:at,  Redness,  Swelling  and  Pain.  —  The  Pro- 
duction OF  Blisters  by  Sunburn.  —  The  Changes  in  the  Ceuxs 
of  an  Injured  Part.  —  The  Cells  which  migrate  from  the 
Blood  vessels  act  as  Phagocytes. — The  Macrophages.  —  The 
MicROPHAGEs.  —  Chemotropism.  —  The  Healino  of  Inflamma- 
tion. —  The  Removal  of  the  Cause.  —  Cell  Repair  and  New 
Formation.  —  New  Formation  of  Blood  vesseus.  —  Acute  and 
Chronic  Inflammation.  —  The  apparently  Purposeful  Char- 
acter OF  the  Changes  in  Inflammation 79 


CHAPTER  V 

Infectious  Diseases.  —  The  Historical  Importance  of  Epi- 
demics OF  DisEA.SE.  —  The  Losses  in  Battle  contrasted  with 
THE  Losses  in  Armies  produced  by  Infectious  Diseases.  — The 
Development  of  Knowledge  of  Epidemics.  —  The  Views  of 
Hippocrates  and  Aristotle.  —  Sporadic  and  Epidemic  Diseases. 
—  The  Theory  of  the  Epidemic  Constitution.  —  Theory  that 
THE  Contagious  Material  is  Living.  —  The  Discovery  of  Bac- 
teria by  Lcewenhceck  in  1675.  —  The  Relation  of  Contagion 
TO  the  Theory  of  Spontaneous  Generation.  —  Needham  and 
Spallanzani.  —  The  Discovert  of  the  Compound  Microscope  in 
1605. — The  Proof  that  a  Living  Organism  is  the  Cause  of  a 
Disease.  —  Anthrax.  —  The  Discovery  of  the  Anthrax  Bacuxus  • 
IN  1851. — The  Cultivation  of  the  Bacillus  by  Koch. — The 
Mode  of  Infection.  —  The  Work  of  Pasteur  on  Anthrax.  — 
The  Importance  of  the  Disease 97 


CH.\PTER  VI 

Classification  of  the  Organisms  which  cause  Disease.  — 
Bacteria:  Size,  Shape,  Structure,  Capacity  for  Growth,  Multi- 
plication AND  Spore  Formation.  —  The  ARTinriAL  Cultivation 
of  Bacteria.  —  The  Importance  of  Bacteria  in  Nature.  —  Va- 
BiATio.vs  IN  Bacteria.  —  Saprophytic  and  Parasitic  Forms.  — 
Protozoa.  —  Structure  more  complicated  than  that  of  Bacteria. 
—  Distribution  in  Nature.  —  Growth  and  Multiplication.  — 
Conjugation  and  Sexual  Reproduction.  —  Spore  Formation.  — 
The  Necessity  fob  a  Fluid  Environment.  — The  Food  of  Proto- 
BOA.  —  Parasitism.  —  The  Ultra-microscopic  or  Filterable  Oh- 
GANIS.WS.  —  The  Limitation  of  the  Microscopic.  —  Porcelain 
Filters  to  separate  Organisms  from  a  Fluid.  —  Foot  and 
Mouth  Disease  produced  by  an  Ultra-microscopic  Organism.  — 
Otbeb  Diseases  so  produced.  —  Do  New  Diseases  appear  ?    .   . 


CONTENTS  vii 

CHAPTER  VII 

Page 
The  Natube  of  Infection.  —  The  Invasion  of  the  Body 
FBOM  ITS  Surfaces.  —  The  Protection  of  these  Surfaces.  —  Can 
Bacteria  pass  through  an  Uninjured  Surface  ?  —  Infection 
FROM  Wounds.  —  The  Wounds  in  Modern  Warfare  less  Prone  to 
Infection.  —  The  Relation  of  Tetanus  to  Wounds  caused  by 
the  Toy  Pistol.  —  The  Primary  Focus  or  Atrium  of  Infection.  — 
The  Dissemination  of  Bacteria  in  the  Body.  —  The  Different 
Degrees  of  Resistance  to  Bacteria  shown  by  the  V.\riou8 
Organs.  —  Mode  of  Action  of  Bacteria.  —  Toxin  Production.  — 
The  Resistance  of  the  Body  to  Bacteria.  —  Conflict  between 
Parasite  and  Host.  —  On  both  Sides  Means  of  Offense  and 
Defense.  —  Phagocytosis. — The  Destruction  of  Bacteria  by 
the  Blood.  —  The  Toxic  Bacterial  Diseases.  —  Toxin  and  Anti- 
toxin. —  Immunity.  —  The  Theory  of  Ehrlich 135 

CHAPTER  VIII 

Secondary,  Terminal  and  Mixed  Infections.  —  The  Exten- 
sion OF  Infection  in  the  Individual.  —  Tuberculosis.  —  The  Tu- 
bercle Bacillus.  —  Frequency  of  the  Disease.  —  The  Primary 
Foci.  —  The  Extension  of  Bacilli.  —  The  Discharge  of  Ba- 
cilli from  the  Body.  —  Influence  of  the  Seat  of  Disease  on  the 
Discharge  of  Bacilli.  —  The  Intestinal  Diseases.  —  Modes  of 
Infbxtion.  —  Infection  by  Sputum  Spray.  —  Infection  of  Water 
Supplies.  —  Extension  of  Infection  by  Insects.  —  Tbypan.vsome 
Diseases.  —  Sleeping  Sickness.  —  Malaria.  —  The  Part  pl.\yed 
BY  Mosquitoes.  —  Parasitism  in  the  Mosquito.  —  Infection  as 
influenced  by  Habits  and  Customs.  —  Hookworm  Disease.  — 
Interrelation  between  Human  and  Animal  Diseases.  —  Plague. 
—  Part  played  by  Rats  in  Transmission.  —  The  Present  Epi- 
DEBUC  or  Plague 159 

CHAPTER  IX 

Disease  Carriers.  —  The  Relation  between  Sporadic  Cases 
OF  Infectious  Disease  and  Epidemics.  —  Smallpox.  —  Cerebro- 
spinal Meningitis.  —  Polyomyelitis.  —  Variation  in  the  Suscep- 
tibility of  Individuals.  —  Conditions  which  may  Influence  Sus- 
ceptibility. —  Racial  Susceptibility.  —  Influence  of  Age  and 
Se.x.  —  Occupation  and  Environment.  —  The  Age  Period  of 
Infectious  Diseases 185 

CHAPTER  X 

Inheritance  as  a  Factor  in  Disease.  —  The  Process  op  Cell 
Multiplication.  —  The  Sexual  Cells  differ  from  the  other 
Cells  of  the  Body.  —  Infection  of  the  Ovum.  —  Intrauterine 
Infection.  — The  Placenta  as  a  Barrier  to  Infection.  — Vari- 
ations AND  Mutations.  —  The  Inheritance  of  Susceptibility  to 
Disease.  —  The  Influence  of  Alcoholism  in  the  Parents  on  the 
Descendants.  —  The  Heredity  of  Nervous  Diseases.  —  Trans- 
mission of  Disease  bit  the  Female  only.  —  Hemophilia.  —  The 
Inheritance  of  Malformations.  —  The  Causes  of  Malforma- 
tions. —  Maternal  Impressions  hate  no  Influence.  —  Eugenics.     197 


viii  CONTENTS 

CHAPTER  XI 

Page 
Chronic  Diseases.  —  Disease  of  the  Heart  as  an  Example. 

—  The  Structitke  and  Fdnction  of  the  Heart.  —  The  Action  of 
THE  Valves.  —  The  Production  op  Heart  Disease  nv  Infection. 

—  The  Conditions  Produced  in  the  Valves.  —  The  Manner  in 
WHICH  Disease  of  the  Valves  interferes  with  their  Function. 

—  The  Compensation  of  Injury  by  Increased  Action  of  Heart.  — 
The  Enlargement  of  the  Heart.  —  The  Result  of  Imper- 
fect Work  of  the  Heart.  —  Venous  Congestion.  —  Dropsy.  — 
Chronic  Diselase  of  the  Nervous  System.  —  Insanity.  —  Rela- 
tion Between  Insanity  and  Criminality.  —  Alcoholism  and 
Syphilis  Frequent  Causes  op  Insanity.  —  The  Direct  and  In- 
direct Causes  of  Nervous  Diseases.  —  The  Relation  between 
Social  Life  and  Nervous  Diseases.  —  Functional  and  Organic 
Disease.  —  Neurasthenia 219 

CHAPTER  "Xll 

The  Rapid  Development  of  Medicine  in  the  Last  Fifty  Years. 

—  The  Influence  op  Darwin.  —  Preventive  Medicine.  —  The 
Dissemination  of  Medical  Knowledge.  —  The  Development  of 
Conditions  in  Recent  Years  which  act  as  Factors  of  Disease.  — 
Factory  Life.  —  Urban  Life.  —  The  Increase  of  Communication 
BETWEEN  Peoples.  —  The  Introduction  of  Plant  Parasites.  — 
The  Increase  in  Asylum  Life.  —  Infant  Mortality.  —  Wealth 

AND  Poverty  as  Factors  in  Disease      241 

Glossary 250 

Index      252 


DISEASE  AND  ITS  CAUSES 


CHAPTER  I 

Definition  of  Disease.  —  Characteristics  of  Living 
Matter.  —  Cells  as  the  Living  Units.  —  Amceba  as 
Type  of  a  Unicellular  Animal. — The  Relation  of  Liv- 
ing Matter  to  the  Enxironment.  —  Capacity  of  Adap- 
tation to  the  Environment  shown  by  Living  Matter. 
—  Individuality  of  Living  Matter.  —  The  Causes  of 
Disease.  —  Extrinsic.  —  The  Relation  of  the  Human 
Body  to  the  Environment.  —  The  Surfaces  of  the 
Body.  —  The  Increase  of  Surface  by  Gland  Forma- 
tion. —  The  Real  Interior  of  the  Body  represented 
BY  the  Various  Structures  placed  between  the  Sur- 
•  FACES.  —  The  Fluids  of  the  Body.  —  The  Nervous 
System.  —  The  Heart  and  Blood-vessels.  —  The  Cells 
of  the  Blood.  —  The  Ductless  Glands. 

There  is  great  difficulty,  in  the  case  of  a  sub- 
ject so  large  and  complex  as  is  disease,  in  giving 
a  definition  which  will  be  accurate  and  compre- 
hensive. Disease  may  be  defined  as  "A  change 
produced  in  living  things  in  consequence  of  which 
they  are  no  longer  in  harmony  with  their  environ- 
ment." It  is  evident  that  this  conception  of  dis- 
ease is  inseparable  from  the  idea  of  life,  since  only 
a  living  thing  can  become  diseased.  In  any  dead 
body  there  has  been  a  preexisting  disease  or  in- 
jury, and,  in  consequence  of  the  change  produced, 
that  particular  form  of  activity  which  constitutes 
9 


10         DISEASE  AND   ITS  CAUSES 

life  has  ceased.  Changes  such  as  putrefaction 
take  place  in  the  dead  body,  but  they  are  changes 
which  would  take  place  in  any  mass  similarly 
constituted,  and  are  not  influenced  by  the  fact 
that  the  mass  was  once  living.  Disease  may  also 
be  thought  of  as  the  negation  of  the  normal. 
There  is,  however,  in  living  things  no  definite 
type  for  the  normal.  An  ideal  normal  type  may 
be  constructed  by  taking  the  average  of  a  large 
number  of  individuals;  but  any  single  individ- 
ual of  the  group  will,  to  a  greater  or  less  extent, 
depart  from  it.  No  two  individuals  have  been 
found  in  whom  all  the  Bertillon  measurements 
agree.  Diseasie  has  reference  to  the  individual; 
conditions  which  in  one  individual  would  be  re- 
garded as  disease  need  not  be  so  regarded  in 
another.  Comparisons  between  health  and  dis- 
ease, the  normal  and  the  abnormal,  must  be  made 
not  between  the  ideal  normal  and  abnormal,  but 
between  what  constitutes  the  normal  or  usual  and 
the  abnormal  in  a  particular  individual. 

The  conception  of  disease  is  so  inseparably 
associated  with  that  of  life  that  a  brief  review  of 
the  structure  and  properties  of  living  things  is 
necessary  for  the  comprehension  of  the  definition 
which  has  been  given.  Living  matter  is  subject 
to  the  laws  which  govern  matter,  and  like  matter 
of  any  other  sort  it  is  composed  of  atoms  and 
molecules.  There  is  no  force  inherent  in  living 
matter,  no  vital  force  independent  of  and  differing 


DISEASE  AND  ITS  CAUSES         11 

from  the  cosmic  forces;  the  energy  which  living 
matter  gives  off  is  counterbalanced  by  the  energy 
which  it  receives.  It  undergoes  constant  change, 
and  there  is  constant  interchange  with  the  environ- 
ment. The  molecules  which  compose  it  are  con- 
stantly undergoing  change  in  their  number,  kind 
and  arrangement.  Atom  groups  as  decomposition 
products  are  constantly  given  off  from  it,  and  in 
return  it  receives  from  without  other  atom  groups 
with  which  it  regenerates  its  substance  or  in- 
creases in  amount.  All  definitions  of  life  convey 
this  idea  of  activity.  Herbert  Spencer  says, 
"Life  is  the  continuous  adjustment  of  internal 
relations  to  external  conditions."  The  molecules 
of  the  substances  forming  the  living  material  are 
large,  complex  and  unstable,  and  as  such  they 
constantly  tend  to  pass  from  the  complex  to  the 
simple,  from  unstable  to  stable  equilibrium. 
The  elementary  substances  which  form  living 
material  are  known,  but  it  has  hitherto  not  been 
found  possible  artificially  so  to  combine  these 
substances  that  the  resulting  mass  will  exhibit 
those  activities  which  we  call  the  phenomena  of 
life.  The  distinction  between  living  and  non- 
living matter  is  manifest  only  when  the  sum  of  the 
activities  of  the  living  matter  is  considered;  any 
single  phenomenon  of  the  living  may  appear  also 
in  the  non-living  material.  Probably  the  most 
distinguishing  criterion  of  living  matter  is  found 
in  its  individuality,  which  undoubtedly  depends 


12         DISEASE  AND   ITS  CAUSES 

upon  differences  in  structure,  whether  physical 
or  chemical,  between  the  different  units. 

Certain  conditions  are  essential  for  the  con- 
tinued existence  of  living  matter.  It  must  be  sur- 
rounded by  a  fluid  or  semi-fluid  medium  in  order 
that  there  may  be  easy  interchange  with  the 
environment.  It  must  constantly  receive  from 
the  outside  a  supply  of  energy  in  the  form  of 
food,  and  substances  formed  as  the  result  of  the 
intracellular  chemical  activity  must  be  removed. 
In  the  case  of  many  animals  it  seems  as  though 
the  necessity  of  a  fluid  environment  for  living 
matter  did  not  apply,  for  the  superficial  cells 
of  the  skin  have  no  fluid  around  them;  these 
cells,  however,  are  dead,  and  serve  merely  a 
mechanical  or  protective  purpose.  All  the  liv- 
ing cells  of  the  skin  and  all  the  cells  beneath 
this  have  fluid  around  them. 

Living  matter  occurs  always  in  the  form  of 
small  masses  called  "cells,"  which  are  the  living 
units.  The  cells  vary  in  form,  structure  and  size, 
some  being  so  large  that  they  can  be  seen  with 
the  naked  eye,  while  others  are  so  small  that  they 
cannot  be  distinctly  seen  with  the  highest 
power  of  the  microscope.  The  living  thing  or 
organism  may  be  composed  of  a  single  cell  or, 
in  the  case  of  the  higher  animals  and  plants, 
may  be  formed  of  great  numbers  of  cells,  those 
of  a  similar  character  being  combined  in  masses 
to  form    organs  such  as   the   liver   and   brain. 


DISEASE  AND   ITS  CAUSES 


13 


In  each  cell  there  is  a  differentiated  area  con- 
stituting a  special  structure,  the  nucleus,  which 
contains  a  peculiar  material  called  "chromatin," 
The  nucleus  has  chiefly  to  do  with  the  multi- 
plication of  the  cell  and  contains  the  factors 
which  determine  heredity.  The  mass  outside  of 
the  nucleus  is  termed  "cytoplasm,"  and  this  may 
be  homogeneous  in  appearance  or  may    contain 


.-?^^^ 


Fig.    1.  —  Diagram    op 
CELL.     1.    Cell  membrane. 
Ti    •      2.  Cell  substance   or  cyto- 
plasm.   3.  Nucleus.    4.  Nu- 
clear membrane.     5.    Nu- 


granules.    On  the  outside 
there  is  a  more  or   less 
definite    cell    membrane. 
It    is   generally   believed 
that  the  cell  material  has 
a  semi-fluid  or  gelatinous 
consistency   and    is   con- 
tained   within    an   intra- 
cellular meshwork 
an    extraordinarily   com 
plex    mass,    whether    re-  ^i^^^^^^- 
garded  from    a   chemical  or   physical  point  of 
view.    (Fig.  1.) 

A  simple  conception  of  health  and  disease  can 
be  arrived  at  by  the  study  of  these  conditions  in 
a  unicellular  animal  directly  under  a  microscope, 
the  animal  being  placed  on  a  glass  slide.  For  this 
purpose  a  small  organism  called  "Amoeba" 
(Fig.  2),  which  is  commonly  present  in  fresh- 
water ponds,  may  be  used.  This  appears  as  a 
small  mass,  seemingly  of  gelatinous  consistency 
with  a  clear  outline,  the  exterior  part  homogeneous. 


14 


DISEASE  AND  ITS  CAUSES 


the  interior  granular.  The  nucleus,  which  is  seen 
with  difficulty,  appears  as  a  small  vesicle  in  the 
interior.  Many  amoebae  show  also  in  the  in- 
terior a  small  clear  space,  the  contractile  vesicle 
which  alternately  contracts  and  expands,  through 
which  action  the  movement  of  the  intracellular 
fluid  is  facilitated  and  waste  products  removed. 
The  interior  granules  often  change  their  position. 


Fig.  2.  —  Amceba.     1.   Nucleus.     2.   Contractile    vesicle. 
S.   Nutritive  vacuole  containing  a  bacillus. 

showing  that  there  is  motion  within  the  mass. 
The  amoeba  slowly  moves  along  the  surface  of 
the  glass  by  the  extension  of  blimt  processes 
formed  from  the  clear  outer  portion  which  ad- 
here to  the  surface  and  into  which  the  interior 
granular  mass  flows.  This  movement  does  not 
take  place  by  chance,  but  in  definite  directions, 
and  may  be  influenced.  The  amoeba  will  move 
towards  certain  substances  which  may  be  placed 
in  the  fluid  around  it  and  away  from  others.  In 
the  water  in  which  the  amoebae  live  there  are 


DISEASE  AND   ITS   CAUSES  15 

usually  other  organisms,  particularly  bacteria,  on 
which  they  feed.  When  such  a  bacterium  comes 
in  contact  with  an  amoeba,  it  is  taken  into  its 
body  by  becoming  enclosed  in  processes  which 
the  amoeba  sends  out.  The  enclosed  organism 
then  lies  in  a  small  clear  space  in  the  amoeba,  sur- 
rounded by  fluid  which  has  been  shown  to  differ 
in  its  chemical  reaction  from  the  general  fluid  of 
the  interior.  This  clear  space,  which  may  form 
at  any  point  in  the  body,  corresponds  to  a  stomach 
in  a  higher  animal  and  the  fluid  within  it  to  the 
digestive  fluid  or  gastric  juice.  After  a  time  the 
enclosed  organism  disappears,  it  has  undergone 
solution  and  is  assimilated;  that  is,  the  sub- 
stances of  which  its  body  was  composed  have 
been  broken  up,  the  molecules  rearranged,  and 
a  part  has  been  converted  into  the  substance  of 
the  amoeba.  If  minute  insoluble  substances,  such 
as  particles  of  carmine,  are  placed  in  the  water, 
these  may  also  be  taken  up  by  the  amoeba;  but 
they  undergo  no  change,  and  after  a  time  they  are 
cast  out.  Under  the  microscope  only  the  gross 
vital  phenomena,  motion  of  the  mass,  motion 
within  the  mass,  the  reception  and  disintegration 
of  food  particles,  and  the  discharge  of  inert  sub- 
stances can  be  observed.  The  varied  and  active 
chemical  changes  which  are  taking  place  cannot 
be  observed. 

Up  to  the  present  it  has  been  assumed  that 
the  environment  of  the  amoeba  is  that  to  which 


16         DISEASE  AND   ITS    CAUSES 

it  has  become  adapted  and  which  is  favorable  to 
its  existence.  Under  these  conditions  its  struc- 
ture conforms  to  the  type  of  the  species,  as  do 
also  the  phenomena  which  it  exhibits,  and  it  can 
assimilate  food,  grow  and  multiply.  If,  during 
the  observation,  a  small  crystal  of  salt  be  placed 
in  the  fluid,  changes  almost  instantly  take  place. 
Motion  ceases,  the  amoebae  appear  to  shrink 
into  smaller  compass,  and  they  become  more 
granular  and  opaque.  If  they  remain  a  suflS- 
ciently  long  time  in  this  fluid,  they  do  not  regain 
their  usual  condition  when  placed  again  in  fresh 
water.  None  of  the  phenomena  which  character- 
ized the  living  amoebae  appear:  we  say  they  are 
dead.  After  a  time  they  begin  to  disintegrate, 
and  the  bacteria  contained  in  the  water  and  on 
which  the  amoebae  fed  now  invade  their  tissue 
and  assist  in  the  disintegration.  By  varying  the 
duration  of  the  exposure  to  the  salt  water  or  the 
amount  of  salt  added,  a  point  can  be  reached 
where  some,  but  not  all,  of  the  amoebae  are  de- 
stroyed. Whether  few  or  many  survive  depends 
upon  the  degree  of  injury  produced.  Much  the 
same  phenomena  can  be  produced  by  gradually 
heating  the  water  in  which  the  amoebae  are  con- 
tained. It  is  even  possible  gradually  to  accustom 
such  small  organisms  to  an  environment  which 
would  destroy  them  if  suddenly  subjected  to  it, 
but  in  the  process  of  adaptation  many  individuals 
will  have  perished. 


DISEASE  AND  ITS  CAUSES         17 

It  is  evident  from  such  an  experiment  that 
when  a  living  organism  is  subject  to  an  environ- 
ment to  which  it  has  not  become  adapted  and 
which  is  unfavorable,  such  alterations  in  its  struc- 
ture may  be  produced  that  it  is  incapable  of 
living  even  when  it  is  again  returned  to  the  con- 
ditions natural  to  it.  Such  alterations  of  struc- 
ture or  injuries  are  called  the  lesions  of  disease. 
We  have  seen  that  in  certain  individuals  the 
injury  was  suflBcient  to  inhibit  for  a  time  only 
the  usual  manifestations  of  life;  these  returned 
when  the  organism  was  removed  from  the  un- 
favorable conditions,  and  with  this  or  preceding 
it  the  organisms,  if  visibly  altered,  regained  the 
usual  form  and  structure.  We  may  regard  this  as 
disease  and  recovery.  In  the  disease  there  is  both 
the  injury  or  lesion  and  the  derangement  of  vital 
activity  dependent  upon  this.  The  cause  of  the 
disease  acted  on  the  organism  from  without,  it 
was  external  to  it.  Whether  the  injurious  ex- 
ternal conditions  act  as  in  this  case  by  a  change 
in  the  surrounding  osmotic  pressure,  or  by  the 
destruction  of  ferments  within  the  cell,  or  by  the 
introduction  into  the  cell  of  substances  which 
form  stable  chemical  union  with  certain  of  its 
constituents,  and  thus  prevent  chemical  processes 
taking  place  which  are  necessary  for  life,  the  re- 
sult is  the  same. 

The  experiments  with  the  amoebae  show  also 
two  of  the  most  striking  characteristics  of  living 


18         DISEASE  AND   ITS  CAUSES 

matter.  1.  It  is  adaptable.  Under  the  influ- 
ence of  unusual  conditions,  alterations  in 
structure  and  possibly  in  substance,  may  take 
place,  in  consequence  of  which  the  organisms  under 
such  external  conditions  may  still  exhibit  the 
usual  phenomena.  The  organism  cannot  adapt 
itself  to  such  changes  without  undergoing  change 
in  structure,  although  there  may  be  no  evidence 
of  such  changes  visible.  This  alteration  of  struc- 
ture does  not  constitute  a  disease,  provided  the 
harmonious  relation  of  the  organism  with  the 
environment  be  not  impaired.  An  individual 
without  a  liver  should  not  be  regarded  as  diseased, 
provided  there  can  be  such  an  internal  adjust- 
ment that  all  of  the  vital  phenomena  could  go  on 
in  the  usual  manner  without  the  aid  of  this  use- 
ful and  frequently  maligned  organ.  2.  It  is  in- 
dividual. In  the  varying  degrees  of  exposure  to 
unfavorable  conditions  of  a  more  serious  nature 
some,  but  not  all,  of  the  organisms  are  destroyed; 
in  the  slight  exposure,  few;  in  the  longer,  many. 
Unfavorable  conditions  which  will  destroy  all  in- 
dividuals of  a  species  exposed  to  them  must  be 
extremely  rare.^  There  is  no  such  individuality  in 
non-living  things.    In  a  mass  of  sugar  grains  each 

'  They  do,  however,  take  place,  since  within  compara- 
tively few  years  whole  species  have  completely  disappeared; 
for  example,  the  great  auk  and  the  passenger  pigeon.  In 
these  cases  it  is  not  known  what  part  disease  played  in  the 
destruction. 


DISEASE  AND   ITS   CAUSES  19 

grain  shows  just  the  same  characteristics  and  re- 
acts, in  exactly  the  same  way  as  all  the  other  grains 
of  the  mass.  Individuality,  however  expressed, 
is  due  to  structural  variation.  It  is  almost  im- 
possible to  conceive  in  the  enormous  complexity 
of  living  things  that  any  two  individuals,  whether 
they  be  single  cells  or  whether  they  be  formed  of 
cell  masses,  can  be  exactly  the  same.  It  is  not 
necessary  to  assume  in  such  individual  differences 
that  there  be  any  variation  in  the  amount  and 
character  of  the  component  elements,  but  the 
individuality  may  be  due  to  differences  in  the 
atomic  or  molecular  arrangements.  There  are 
two  forms  of  tartaric-acid  crystals  of  precisely 
the  same  chemical  formula,  one  of  which  reflects 
polarized  light  to  the  left,  and  the  other  to  the 
right.  All  the  left-sided  crystals  and  all  the  right- 
sided  are,  however,  precisely  the  same.  The 
number  of  possible  variations  in  the  chemical 
structure  of  a  substance  so  complex  as  is  proto- 
plasm is  inconceivable. 

In  no  way  is  the  individuality  of  living  matter 
more  strongly  expressed  than  in  the  resistance 
to  disease.  The  variation  in  the  degree  of  resist- 
ance to  an  unfavorable  environment  is  seen  in 
every  tale  of  shipwreck  and  exposure.  In  the 
most  extensive  epidemics  certain  individuals  are 
spared;  but  here  care  must  be  exercised  in  inter- 
preting the  immunity,  for  there  must  be  differences 
in  the  degree  of  exposure  to  the  cause  of  the 


20         DISEASE  AND  ITS  CAUSES 

epidemic.  It  would  not  do  to  interpret  the  im- 
munity to  bullets  in  battle  as  due  to  any  indi- 
vidual peculiarity,  save  possibly  a  tendency  in 
certain  individuals  to  remove  the  body  from  the 
vicinity  of  the  bullets;  in  battle  and  in  epidemics 
the  factors  of  chance  and  of  prudence  enter.  No 
other  living  organism  is  so  resistant  to  changes  in 
environment  as  is  man,  and  to  this  resistance  he 
owes  his  supremacy.  By  means  of  his  intelligence 
he  can  change  the  environment.  He  is  able  to 
resist  the  action  of  cold  by  means  of  houses, 
fire  and  clothing;  without  such  power  of  in- 
telligent creation  of  the  immediate  environment 
the  climatic  area  in  which  man  could  live  would 
be  very  narrow.  Just  as  disease  can  be  acquired 
by  an  unfavorable  environment,  man  can  so 
adjust  his  environment  to  an  injury  that  harmony 
will  result  in  spite  of  the  injury.  The  environ- 
ment which  is  necessary  to  compensate  for  an 
injury  may  become  very  narrow.  For  an  indi- 
vidual with  a  badly  working  heart  more  and  more 
restriction  of  the  free  life  is  necessary,  until  finally 
the  only  environment  in  which  life  is  even  toler- 
ably harmonious  is  between  blankets  and  within 
the  walls  of  a  room. 

The  various  conditions  which  may  act  on  an 
organism  producing  the  changes  which  are  neces- 
sary for  disease  are  manifold.  Lack  of  resistance 
to  injury,  incapacity  for  adaptation,  whether  it 
be  due  to  a  congenital  defect  or  to  an  acquired 


DISEASE  AND   ITS  CAUSES 


21 


condition,  is  not  in  itself  a  disease,  but  the  disease 
is  produced  by  the  action  on  such  an  individual 
of  external  conditions  which   may  be   nothing 


Fig.  3.  —  A  section  of  the  skin.  1.  A  hair.  Notice 
there  is  a  deep  depression  of  the  surface  to  form  a  small  bulb 
from  which  the  hair  grows.  2.  The  superficial  or  horny 
layer  of  the  skin;  the  cells  here  are  joined  to  form  a  dense, 
smooth,  compact  layer  impervious  to  moisture.  3.  The 
lower  layer  of  cells.  In  this  layer  new  cells  are  continually 
being  formed  to  supply  those  which  as  thin  scales  are  cast 
oflf  from  the  surface.  4.  Section  of  a  small  vein.  9.  Section 
of  an  artery.  8.  Section  of  a  lymphatic.  The  magnification 
is  too  low  to  show  the  smaller  blood  vessels.  5.  One  of  the 
glands  alongside  of  the  hair  which  furnishes  an  oily  secretion. 
6.  A  sweat  gland.  7.  The  fat  of  the  skin.  Notice  that  hair, 
hair  glands  and  sweat  glands  are  continuous  with  the  surface 
and  represent  a  downward  extension  of  this.  All  the  tissue 
below  2  and  3  is  the  corium  from  which  leather  is  made. 

more  than  those  to  which  the  individuals  of  the 
species  are  constantly  subject  and  which  produce 
no  harm. 


22 


DISEASE  AND   ITS  CAUSES 


All  of  the  causes  of  disease  act  on  the  body  from 
without,  and  it  is  important  to  understand  the 
relations  which  the  body  of  a  highly  developed 
organism  such  as  man  has  with  the  world  external 
to  him.  This  relation  is  effected  by  means  of  the 
various  surfaces  of  the  body.  On  the  outside  is 
the  skin  (Fig.  3),  which  surface  is  many  times 


^  r 


Fig.  4.  —  Diagrammatic  section  op  a  subface  showing 

THE    RELATION    OF   GLANDS   TO    THE  SURFACE.       (a)     Simple   Of 

tubular  gland;    (6)  compound  or  racemose  gland. 

increased  by  the  existence  of  glands  and  such 
appendages  to  the  skin  as  the  hair  and  nails.  A 
gland,  however  complicated  its  structure,  is 
nothing  more  than  an  extension  of  the  surface 
into  the  tissue  beneath  (Fig.  4).  In  the  course 
of  embryonic  development  all  glands  are  formed 
by  an  ingrowth  of  the  surface.  The  cells  which 
line  the  gland  surface  undergo  a  differentiation 


DISEASE  AND   ITS  CAUSES 


23 


in  structure  which  enables  them  to  perform  cer- 
tain definite  functions,  to  take  up  substances 
from  the  same  source  of  supply  and  transform 
them.  The  largest  gland  on  the  external  surface 
of  the  body  is  the  mammary  gland  (Fig.  5)   in 


Fig.  5.  —  A  section  of  the  mammary  gland,  (o)  The 
ducts  of  the  gland,  by  which  the  milk  secreted  by  the  cells 
which  line  all  the  small  openings,  is  conveyed  to  the  nipple. 
All  these  openings  are  continuous  with  the  surface  of  the  skin. 
On  each  side  of  the  large  ducts  is  a  vein  filled  with  blood 
corpuscles. 


which  milk  is  produced;  there  are  two  million 
small,  tubular  glands,  the  sweat  glands,  which 
produce  a  watery  fluid  which  serves  the  purpose 
of  cooling  the  body  by  evaporation;  there  are 
glands  at  the  openings  of  the  hairs  which  produce 


24  DISEASE  AND   ITS  CAUSES 

a  fatty  secretion  which  lubricates  the  hair  and 
prevents  drying,  and  many  others. 

The  external  surface  passes  into  the  interior 


Fig.  6.  —  Photograph  of  a  section  of  the  lung  of  a 
MOUSE.  X  X  are  the  air  tubes  or  bronchi  which  communicate 
with  all  of  the  small  spaces.  On  the  walls  of  the  partitions 
there  is  a  close  network  of  blood  vessels  which  are  separated 
from  the  air  in  the  spaces  by  a  thin  membrane. 

of  the  body  forming  two  surfaces,  one  of  which, 
the  intestinal  canal,  communicates  in  two  places, 
at  the  mouth  and  anus,  with  the  external  surface; 


DISEASE  AND   ITS  CAUSES  25 

and  the  other,  the  genito-urinary  surface,  which 
communicates  with  the  external  surface  at  one 
place  only.  The  surface  of  the  intestinal  canal 
is  much  greater  in  extent  than  the  surface  on  the 
exterior,  and  finds  enormous  extensions  in  the 
lungs  and  in  the  great  glands  such  as  the  liver 
and  pancreas,  which  communicate  with  it  by 
means  of  their  ducts.  The  extent  of  surface  with- 
in the  lungs  is  estimated  at  ninety-eight  square 
yards,  which  is  due  to  the  extensive  infoldings  of 
the  surface  (Fig.  6),  just  as  a  large  surface  of 
thin  cloth  can,  by  folding,  be  compressed  into  a 
small  space.  The  intestinal  canal  from  the  mouth 
to  the  anus  is  thirty  feet  long;  the  circumference 
varies  greatly,  but  an  average  circumference  of 
three  inches  may  safely  be  assumed,  which  would 
give  between  seven  and  eight  square  feet  of  sur- 
face, this  being  many  times  multiplied  by  adding 
the  surfaces  of  the  glands  which  are  connected 
with  it.  A  diagram  of  the  microscopic  structure 
of  the  intestinal  wall  shows  how  little  appreci- 
ation of  \he  extent  of  surface  the  examination 
with  the  naked  eye  gives  (Fig.  7).  By  means  of 
the  intestinal  canal  food  or  substances  necessary 
to  provide  the  energy  which  the  living  tissue 
transforms  are  introduced.  This  food  is  liquefied 
and  so  altered  by  the  action  of  the  various  fluids 
formed  in  the  glands  of  the  intestine  and  poured 
out  on  the  surface,  that  it  can  pass  into  the  in- 
terior of  the  body  and  become  available  for  the 


26 


DISEASE  AND   ITS  CAUSES 


living  cells.  Various  food  residues  representing 
either  excess  of  material  or  material  incapable 
of  digestion  remain  in  the  intestine,  and  after 
undergoing  various  changes,  putrefactive  in 
character,  pass  from  the  anus  as  feces. 

By  means  of  the  lungs,  which  represent  a  part 
of  the  surface,  the  oxygen  of  the  air,  "which  is 


Fig.  7. — A  section  op  the  small  intestine  to  show  the 
LARGE  EXTENT  OF  SURFACE,  (o)  Internal  surface.  The 
small  finger-like  projections  are  the  villi,  and  between  these 
are  small  depressions  forming  tubular  glands. 

indispensable  for  the  life  of  the  cells,  is  taken 
into  the  body  and  carbonic  acid  removed.  The 
interchange  of  gases  is  effected  by  the  blood, 
which,  enclosed  in  innumerable,  small,  thin-walled 
tubes,  almost  covers  the  surface,  and  comes  in 
contact  with  the  air  within  the  lungs,  taking 
from  it  oxygen  and  giving  to  it  carbonic  acid. 


Fig.  8. —  A  longitudinal  section   through   the  midolb 

OF    THE     BODY    SHOWING    THE    EXTERNAL   AND    INTERNAL    SUR- 
FACES  AND    THE    ORGANS. 


1.  The  skull. 

2.  The  brain,  showing  the 
convolutions  of  the  gray  ex- 
terior in  which  the  nerve  cells 
are  most  numerous. 

3.  The  white  matter  in  the 
interior  of  the  brain  formed  of 
nerve  fibres  which  connect  the 
various  parts  of  this. 

4.  The  small  brain  or  cere- 
bellum. 

5.  The  interior  of  the  nose. 
Notice  the  nearness  of  the 
upper  part  of  this  cavity  to 
the  brain. 

6.  The  hard  or  bony  palate 
forming  the  roof  of  the  mouth. 

7.  The  soft  palate  which 
hangs  as  a  curtain  between  the 
mouth  and  the  pharynx. 

8.  The  mouth  cavity. 

9.  The  tongue. 

10.  The  beginning  of  the 
gullet  or  oesophagus. 

11.  The  larynx. 

12.  The  windpipe  or  trachea. 

13.  The   oesophagus. 

14.  The  thyroid  gland. 

15.  The  thymus  gland  or 
sweetbread. 

16.  The  large  vein,  vena 
cava,  which  conveys  the  blood 
from  the  brain  and  upper  body 
into  the  heart. 

17-25.  Lymph  nodes;  17,  of 
the  neck;  25,  of  the  abdomen. 


18.  Cross  section  of  the  arch 
of  the  aorta  or  main  artery  of 
the  body  after  it  leaves  the 
heart. 

19.  The  sternum  or  breast 
bone. 

20.  The  cavity  of  the  heart. 

21.  The  liver. 

22.  The  descending  aorta  at 
the  back  of  the  abdominal 
cavity. 

23.  The  pancreas. 

24.  The  stomach. 

26.  Cross  section  of  the  in- 
testines. 

27.  The  urinary  bladder. 

28.  The  entrance  into  this  of 
the  ureter  or  canal  from  the 
kidney. 

29.  Cross  sections  of  the  pu- 
bic bone. 

30.  The  canal  of  the  urethra 
leading  into  the  bladder. 

31.  The  penis. 

32.  The  s(>inal  cord. 

33.  The  bones  composing  the 
spinal  column. 

34.  The  sacrum.  The  space 
between  this  and  No.  29  is  the 
pelvis. 

35.  The  coccyx  or  extremity 
of  the  back  bone. 

36.  The  rectum. 

37.  The  testicles. 


DISEASE  AND   ITS  CAUSES  27 

The  genito-urinary  surface  is  the  smallest  of 
the  surfaces.  In  the  male  (Fig.  8,  —  27,  28,  30) 
this  communicates  with  the  general  external 
surface  by  the  small  opening  at  the  extremity 
of  the  penis,  and  in  the  female  by  the  opening 
into  the  vagina.  In  its  entirety  it  consists  in  a 
surface  of  wide  extent,  comprising  in  the  male  the 
urethra,  a  long  canal  which  opens  into  the  bladder, 
and  is  continuous  with  ducts  that  lead  into  the 
genital  glands  or  testicles.  The  internal  surface 
of  the  bladder  is  extended  by  means  of  two  long 
tubes,  the  ureters,  into  the  kidneys,  and  receives 
the  fluid  formed  in  these  organs.  In  the  female 
(Fig.  9)  there  is  a  shallow  external  orifice  which 
is  continued  into  the  bladder  by  a  short  canal, 
the  urethra,  the  remaining  urinary  surface  being 
the  same  as  in  the  male;  the  external  opening 
also  is  extended  into  the  short,  wide  tube  of 
the  vagina,  which  is  continuous  with  the  canal  of 
the  uterus.  This  canal  is  continued  on  both 
sides  into  the  Fallopian  tubes  or  oviducts.  There 
is  thus  in  the  female  a  more  complete  separation 
of  the  urinary  and  the  genital  surfaces  than  in 
the  male.  Practically  all  of  the  waste  material 
of  the  body  which  results  from  cell  activity  and 
is  passed  from  the  cells  into  the  fluid  about  them 
is  brought  by  the  blood  to  the  kidneys,  and  re- 
moved by  these  from  the  blood,  leaving  the  body 
as  urine. 

Between  these  various  surfaces  is  the  real  in- 


28         DISEASE  AND   ITS  CAUSES 

terior  of  the  body,  in  which  there  are  many  sorts 
of  living  tissues,^  each,  of  which,  in  addition  to 


Fig.  9.  —  A  LONomjDiNAL  section  through  the  feualb 

PELVIS. 

1.  The  Fallopian  tube  which  forms  the  coimection  be- 

tween the  ovary  and  the  uterus. 

2.  The  ovary. 

3.  The  body  of  the  uterus. 

4.  The  uterine  canal. 

5.  The  urinary  bladder  represented  as  empty. 

6.  The  entrance  of  the  ureter. 

7.  The  pubic  bone. 

8.  The  urethra. 

9.  The  vagina. 

10.  The  common  external  opening  or  vulva. 

11.  The  rectum  and  anus. 

*  A  tissue  represents  an  aggregate  of  similar  cells  with 
the  intercellular  substances  in  relation  with  these  as  connec- 
tive tissue,  muscular  tissue,  etc.    Where  such  cell  aggregates 


DISEASE  AND   ITS  CAUSES 


29 


maintaining  itself,  has  some  function  necessary  for 
the  maintenance  of  the  body  as  a  whole.  Many  of 
these  tissues  have  for  their  main  purpose  the  ad- 


FiG.  10.  -  The  lungs  and  windpipe.  Parts  of  the  lungs 
have  been  removed  to  show  the  branching  of  the  air  tubes 
or  bronchi  which  pass  into  them.  All  the  tubes  and  the 
surfaces  of  the  lungs  communicate  with  the  inner  surface 
of  the  body  through  the  larynx. 

justment  and  coordination  of  the  activities  of  the 
different  organs  to  the  needs  of  the  organism  as 
a  whole.    The  activity  of  certain  of  the  organs  is 

are  localized  and  where  the  cells  are  arranged  in  structures 
having  definite  form  and  size  and  performing  a  definite  func- 
tion, it  is  customary  to  designate  such  structures  as  organs, 
as  the  brain,  liver,  etc. 


30         DISEASE  AND   ITS  CAUSES 

essential  for  the  maintenance  of  life;  without 
others  life  can  exist  for  a  time  only;  and  others, 
such  as  the  genital  glands,  while  essential  for  the 
preservation  of  the  life  of  the  species,  are  not  es- 
sential for  the  individual.  There  is  a  large  amount 
of  reciprocity  among  the  tissues;  in  the  case  of 
paired  organs  the  loss  of  one  can  be  made  good  by 
increased  activity  of  the  remaining,  and  certain 
of  the  organs  are  so  nearly  alike  in  function  that 
a  loss  can  be  compensated  for  by  an  increase  or 
modification  of  the  function  of  a  nearly  related 
organ.  The  various  internal  parts  are  connected 
by  means  of  a  close  mesh  work  of  interiacing 
fibrils,  the  connective  tissue,  support  and  strength 
being  given  by  the  various  bones.  Everywhere 
enclosing  all  living  cells  and  penetrating  into  the 
densest  of  the  tissues  there  is  fluid.  We  may 
even  consider  the  body  between  the  surfaces  as 
a  bag  filled  with  fluid  into  which  the  various  cells 
and  structures  are  packed. 

The  nervous  system  (Fig.  8)  represents  one 
of  the  most  important  of  the  enclosed  organs. 
It  serves  an  important  function,  not  only  in  regu- 
lating and  coordinating  all  functions,  but  by 
means  of  the  special  senses  which  are  a  part  of 
it,  the  relations  of  the  organism  as  a  whole  with 
the  environment  are  adjusted.  It  consists  of  a 
large  central  mass,  the  brain  and  spinal  cord, 
which  is  formed  in  the  embryo  by  an  infolding 
of  the  external  surface,  much  in  the  same  way 


DISEASE  AND  ITS  CAUSES         31 

that  a  gland  is  formed;  but  the  connection  with 
the  surface  is  lost  in  further  development  and  it 
becomes  completely  enclosed.  Connected  with 
the  central  nervous  mass,  forming  really  a  part 
of  it  and  developing  from  it,  are  the  nerves,  which 
appear  as  white  fibrous  cords  and  after  divid- 
ing and  subdividing,  are  as  extremely  fine  mi- 
croscopic filaments  distributed  to  all  parts  of 
the  body.  By  means  of  the  nerves  all  impres- 
sions are  conveyed  to  the  brain  and  spinal  cord; 
all  impulses  from  this,  whether  conscious  or 
unconscious,  are  conveyed  to  the  muscles  and 
other  parts.  The  brain  is  the  sole  organ  of 
psychical  life;  by  means  of  its  activity  the  impres- 
sions of  the  external  world  conveyed  to  it  through 
the  sense  organs  are  converted  into  consciousness. 
Whatever  consciousness  is,  and  on  this  much  has 
been  written,  it  proceeds  from  or  is  associated 
with  the  activity  of  the  brain  cells  just  as  truly 
as  the  secretion  of  gastric  juice  is  due  to  the 
activity  of  the  cells  of  the  stomach.  The  activity 
of  the  nervous  system  is  essential  for  extra-uterine 
life;  life  ceases  by  the  cessation  of  circulation 
and  respiration  when  either  the  whole  or  certain 
small  areas  of  its  tissue  are  destroyed.  In  intra- 
uterine life,  with  the  narrow  and  unchanging  en- 
vironment of  the  fluid  within  the  uterine  cavity 
which  encloses  the  foetus,  life  is  compatible  with 
the  absence  or  rudimentary  develor^ment  of  the 
nervous  system.     The  foetus  in   this   condition 


32         DISEASE  AND  ITS  CAUSES 

may  be  otherwise  well  developed,  and  it  would  be 
not  a  misuse  of  words  to  say  that  it  was  healthy, 
since  it  is  adjusted  to  and  in  harmony  with  its 
narrow  environment,  but  it  would  not  be  normal. 
The  intra-uterine  life  of  the  unborn  child,  it  must 
be  remembered,  is  carried  out  by  the  transmis- 
sion of  energy  from  the  mother  to  the  foetus  by 
means  of  the  close  relation  between  the  maternal 
and  foetal  circulation.  It  is  only  when  the  free 
existence  demands  activities  not  necessary  in 
intra-uterine  life  that  existence  without  a  central 
nervous  system  becomes  impossible. 

It  is  essential  in  so  complicated  a  structure  as 
the  body  that  some  apparatus  should  exist' to  pro- 
vide for  the  interchange  of  material.  The  innu- 
merable cell  units  of  the  body  must  have  mate- 
rial to  provide  energy,  and  useless  material  which 
results  from  their  activity  must  be  removed. 
A  household  might  be  almost  as  much  embar- 
rassed by  the  accumulation  of  garbage  and  ashes 
as  by  the  absence  of  food  and  coal.  The  food, 
which  is  taken  into  the  alimentary  canal  and 
converted  by  the  digestive  fluids  into  material 
more  directly  adapted  to  the  uses  of  cells,  must 
be  conveyed  to  them.  A  supply  of  oxygen  is 
essential  for  the  life  of  the  cells,  and  the  supply 
which  is  given  by  respiration  must  be  carried 
from  the  lungs  to  every  cell  of  the  body.  All 
this  is  effected  by  the  circulation  of  the  blood, 
which  takes  place  in  the  system  of  branching 


DISEASE  AND   ITS   CAUSES 


33 


closed  tubes  in  which  the  blood  remains  (Fig. 
11).  Certain  of  these  tubes,  the  arteries,  have 
strong  and  elastic  walls  and  serve  to  convey  and 


Fig.  11.  —  A  diagrammatic  view  of  the  blood  vessels. 
An  artery  (a)  opens  into  a  system  of  capillaries,  (c)  and  after 
passing  through  these  collects  into  a  vein  (6).  Notice  that 
the  capillaries  connect  with  other  vascular  territories  at 
numerous  points  (d).  If  the  artery  (a)  became  closed  the 
capillaries  which  it  supplies  could  be  filled  by  blood  coming 
from  other  sources. 

distribute  the  blood  to  the  different  organs  and 
tissues.  From  the  ultimate  branches  of  the  ar- 
teries the  blood  passes  into  a  close  network  of 
tubes,  the  capillaries,  which  in  enormous  numbers 


34         DISEASE  AND  ITS  CAUSES 

are  distributed  in  the  tissues  and  have  walls  so 
thin  that  they  allow  fluid  and  gaseous  interchange 
between  their  contents  and  the  fluid  around  them 
to  take  place.  The  blood  from  the  capillaries  is 
then  collected  into  a  series  of  tubes,  the  veins,  by 
which  it  is  returned  to  the  heart.  This  circulation 
is  maintained  by  means  of  a  pumping  organ  or 
heart,  which  receives  the  blood  from  the  veins  and 
by  the  contraction  of  its  powerful  walls  forces  this 
into  the  arteries,  the  direction  of  flow  being  deter- 
mined as  in  a  pump,  by  a  system  of  valves.  The 
waste  products  of  cell  life  pass  from  the  cells  into 
the  fluid  about  them,  and  are  in  part  directly  re- 
turned into  the  blood,  but  for  the  greater  part 
pass  into  it  indirectly  through  another  set  of  ves- 
sels, the  lymphatics.  These  are  thin-walled  tubes 
which  originate  in  the  tissues,  and  in  which  there 
is  a  constant  flow  towards  the  heart,  maintained 
by  the  constant  but  varying  pressure  of  the 
tissue  around  them,  the  direction  of  flow  being 
maintained  by  numerous  valves.  The  colorless 
fluid  within  these  vessels  is  termed  "lymph."  At 
intervals  along  these  tubes  are  small  structures 
termed  the  lymph  nodes,  which  essentially  are 
filters,  and  strain  out  from  the  fluid  substances 
which  might  work  great  injury  if  they  passed 
into  the  blood.  Between  the  capillary  vessels 
and  the  lymphatics  is  the  tissue  fluid,  in  which 
all  the  exchange  takes  place.  It  is  constantly 
added  to  by  the  blood,  and  returns  fluid  to  the 


DISEASE  AND   ITS   CAUSES  35 

blood  and  lymph;  it  gives  material  to  the  cells 
and  receives  material  from  them. 

In  addition  to  the  strength  and  elasticity  of 
the  wall  of  the  arteries,  which  enables  them  to 
resist  the  pressure  of  the  blood,  they  have  the 
power  of  varying  their  calibre  by  the  contraction 
or  expansion  of  their  muscular  walls.  Many  of 
the  organs  of  the  body  function  discontinuously, 
periods  of  activity  alternating  with  comparative 
repose;  during  the  period  of  activity  a  greater 
blood  supply  is  demanded,  and  is  furnished  by 
relaxation  of  the  muscle  fibres  which  allows  the 
calibre  to  increase,  and  with  this  the  blood  flow 
becomes  greater  in  amount.  Each  part  of  the 
body  regulates  its  supply  of  blood,  the  regulation 
being  effected  by  means  of  nerves  which  control 
the  tension  of  the  muscle  fibres.  The  circulation 
may  be  compared  with  an  irrigation  system  in 
which  the  water  supply  of  each  particular  field 
is  regulated  not  by  the  engineer,  but  by  an  auto- 
matic device  connected  with  the  growing  crop 
and  resj)onding  to  its  demands. 

The  blood  consists  of  a  fluid,  the  blood  plasma, 
in  which  numerous  cells  are  contained.  The  most 
numerous  of  these  are  small  cup-shaped  cells 
which  contain  a  substance  called  haemoglobin , 
to  which  the  red  color  of  the  blood  is  due.  There 
are  five  miUion  of  these  cells  in  a  cubic  millimeter 
(a  millimeter  is  .03937  of  an  inch),  giving  a  total 
number   for   the   average   adult   of   twenty-five 


36 


DISEASE  AND  ITS  CAUSES 


trillion.  The  surface  area  of  all  these,  each  being 
one  thirty-three  hundredth  of  an  inch  in  diam- 
eter, is  about  thirty-three  hundred  square  yards. 
The  haemoglobin  which  they  contain  combines 
in  the  lungs  with  the  oxygen  in  the  inspired  air, 
and  they  give  up  this  indispensable  substance  to 
the  cells  everywhere  in  the  body.    There  are  also 


Fig.  12.  —  The  various  cells  in  the  blood,  (a)  The 
red  blood  cells,  single  and  forming  a  roll  by  adhering  to  one 
another;  (6)  different  forms  of  the  white  blood  cells;  those 
marked  "  1 "  are  the  must  numerous  and  are  phagocytic  for 
bacteria. 


eight  thousand  leucocytes  or  colorless  cells  in  a 
cubic  millimeter  of  blood,  this  giving  a  total 
number  of  four  billion  in  the  average  adult,  and 
these  vary  in  character  and  in  relative  numbers 
(Fig.  12).  The  most  numerous  of  these  are  round 
and  slightly  larger  than  the  red  cells;  they  have 
a  nucleus  of  peculiar  shape  and  contain  granules 
of  a  definite  character.    These  cells  serve  an  im- 


DISEASE  AND  ITS  CAUSES         37 

portant  part  in  infectious  diseases  in  devouring 
and  destroying  parasites.  They  have  power  of 
active  independent  motion  and  somewhat  re- 
semble certain  of  the  free  living  unicellular  organ- 
isms. The  blood  plasma,  when  taken  from  the 
vessels,  clots  or  passes  from  a  fluid  into  a  gelati- 
nous or  semi-solid  condition,  which  is  due  to  the 
formation  within  it  of  a  network  of  fine  threads 
termed  fibrin.  It  is  by  means  of  the  clotting  of  the 
blood  that  the  escape  of  blood  from  ruptured 
vessels  is  arrested. 

Several  of  the  organs  of  the  body,  in  addition 
to  the  formation  of  secretions  which  are  dis- 
charged on  the  surfaces  by  means  of  their  ducts, 
produce  also  substances  which  pass  directly  into 
the  blood  or  lymph,  and  have  an  influence  in 
stimulating  or  otherwise  regulating  the  activity 
of  other  organs.  There  are  also  certain  organs 
of  glandular  structure  which  are  called  the 
ductless  glands;  these  are  not  connected  with 
the  surface  and  all  their  secretion  passes  into  the 
blood.  It  is  a  part  of  recent  knowledge  that  the 
substances  produced  in  these  glands  are  of  great 
importance  for  the  body,  some  of  them  even 
essential  for  the  maintenance  of  life.  In  front 
of  the  neck  is  such  an  organ,  the  thyroid  gland 
(Fig.  8,  14).  Imperfect  development  or  absence 
of  this  organ,  or  an  inactive  condition  of  it,  pro- 
duces in  the  child  arrested  growth  and  deficient 
mental  development  known  as  cretinism,  and  in 


215143 


38         DISEASE  AND   ITS  CAUSES 

the  adult  the  same  condition  gives  rise  to  mental 
deterioration,  swelling  of  the  skin,  due  to  a  greater 
content  of  water,  and  loss  of  hair.  This  deficiency 
in  the  production  of  thyroid  secretion  can  be 
made  good  and  the  symptoms  removed  by  feed- 
ing the  patient  with  similar  glands  removed  from 
animals.  The  very  complex  disease  known  as 
exophthalmic  goitre,  and  shown  by  irregular 
and  rapid  action  of  the  heart,  protruding  eye- 
balls and  a  variety  of  mental  symptoms,  is  also 
associated  with  this  gland,  and  occasioned  not 
by  a  deficiency  but  by  an  excess  or  perversion  of 
its  secretion. 

Adjoining  the  thyroid  there  are  four  small 
glands,  the  parathyroids,  each  about  the  size 
of  a  split  pea.  The  removal  of  these  glands  in 
animals  produces  a  condition  resembling  acute 
poisoning  accompanied  by  spasmodic  contraction 
of  the  muscles.  A  small  glandular  organ  at  the 
base  of  the  brain,  the  pituitary  body,  produces 
a  secretion,  one  of  the  most  marked  properties 
of  which  is  a  control  of  growth,  particularly 
that  of  the  bones.  Most  cases  of  giantism, 
combined  as  they  are  with  imperfect  mentality, 
are  due  to  disease  of  this  gland.  There  are  glands 
near  the  kidney  which  regulate  the  pressure 
of  the  blood  in  the  arteries  by  causing  contraction 
of  their  muscular  walls.  The  sexual  character- 
istics in  the  male  and  female  are  due  to  an  inter- 
nal secretion  produced  by  the  respective  sexual 


DISEASE  AND   ITS   CAUSES  39 

glands  which  affects  growth,  body  development 
and  mentality. 

So  is  the  body  constituted.  A  series  of  surfaces, 
all  connected,  of  enormous  size,  which  enclose 
a  large  number  of  organs  and  tissues,  the  activities 
of  which  differ,  but  all  are  coordinated  to  serve 
the  purposes  of  the  organism  as  a  whole.  We 
should  think  of  the  body  not  as  an  assemblage 
of  more  or  less  independent  entities,  but  as  a  single 
organism  in  which  all  parts  are  firmly  knit  to- 
gether both  in  structure  and  in  function,  as  are 
the  components  of  a  single  cell. 


CHAPTER  II 

No  Shabp  Line  of  Demarkation  between  Health  and 
Disease.  —  The  Functional  Nutritive  and  Forma- 
tive Activities  of  Cells.  —  Destruction  and  Repair 
Constant  Processes  in  Living  Matter.  —  Injuries  to 
THE  Body.  —  The  Effect  of  Heat.  —  The  Action  of 
Poisons.  —  The  Lesions  op  Disease.  —  Repair.  —  The 
Laws  Governing  Repair.  —  Relation  of  Repair  to 
Complexity  of  Structure  and  Age.  —  The  Reserve 
Force  of  the  Body.  —  Compensatory  Processes  in  the 
Body.  —  Old  Age.  —  The  Diminution  of  Resistance 
TO  the  Effect  of  the  Environment  a  Prominent 
Factor  in  Old  Age.  —  Death.  —  How  brought  about. 
—  Changes  in  the  Body  after  Death. — The  Recog- 
nition OF  Death. 

There  is  no  sharp  line  separating  health  from 
disease;  changes  in  the  tissues  of  the  same  nature, 
or  closely  akin  to  those  which  are  found  in  dis- 
ease, are  constantly  occurring  in  a  state  of  health. 
The  importance  of  parasites  in  causing  disease 
has  led  to  the  conception  of  disease  as  almost 
synonymous  with  parasitism;  but  it  must  be 
remembered  that  the  presence  of  parasites  living 
at  the  expense  of  the  body  is  perfectly  consistent 
with  a  state  of  health.  Degeneration,  decay  and 
parasitism  only  become  disease  factors  when  the 
conditions  produced  by  them  interfere  with  the 
life  which  is  the  normal  or  usual  for  the  individual 

concerned. 

40 


DISEASE  AND   ITS  CAUSES  41 

All  the  changes  which  take  place  in  the  cells 
are  of  great  importance  in  conditions  of  both 
health  and  disease,  for  life  consists  in  coordinated 
cell  activity.  The  activities  of  the  cells  can  be 
divided  into  those  which  are  nutritive,  those 
which  are  functional  and  those  which  are  forma- 
tive. In  the  functional  activity  the  cell  gives 
off  energy,  this  loss  being  made  good  by  the 
receipt  of  new  energy  in  the  form  of  nutritive 
material  with  which  the  cell  renews  itself.  In 
certain  cells  an  exact  balance  seems  to  be  main- 
tained, but  in  those  cells  whose  activity  is  periodic 
function  takes  place  at  the  expense  of  the  cell 
substance,  the  loss  being  restored  by  nutrition 
during  the  period  of  repose.  This  is  shown 
particularly  well  in  the  case  of  the  nerve  cells 
(Fig.  13).  Both  the  functional  and  nutritive 
activity  can  be  greatly  stimulated,  but  they 
must  balance;  otherwise  the  condition  is  that 
of  disease. 

The  formative  activity  of  cells  is  also  essential 
to  the  normal  state.  Destruction  of  cells  is  con- 
stantly taking  place  in  the  body,  and  more  rapidly 
in  certain  tissues  than  in  others.  Dried  and  dead 
cells  are  constantly  and  in  great  numbers  thrown 
off  from  the  surface  of  the  skin:  such  epidermic 
appendages  as  the  hair  and  nails  grow  and  are 
removed,  millions  of  cells  are  represented  in  the 
beard  which  is  daily  removed.  Cells  are  con- 
stantly being  destroyed  on  the  intestinal  surface 


42 


DISEASE  AND   ITS  CAUSES 


and  in  the  glands.  There  is  an  enormous  de- 
struction of  the  blood  cells  constantly  taking 
place,  certain  essential  pigments,  as  that  of  the 
bile,  being  formed  from  the  haemoglobin  which 
the  red  blood  corpuscles  contain  and  which 
becomes  available  on  their  destruction.  All 
such  loss  of  cells  must  be  made  good  by  the 


Fig.  13.  —  Nerve  cells  op  an  English  spabbow.  (o) 
Cells  after  a  day's  full  activity;  (6)  cells  after  a  night's  repose. 
In  (a)  the  cells  and  nuclei  are  shrunken  and  the  smaller  clear 
spaces  in  the  cells  are  smaller  and  less  evident  than  in  (b). 
(Hodge.) 

formation  of  new  ones  and,  as  in  the  case  of  the 
nutritive  and  functional  activity,  the  loss  and 
renewal  must  balance.  The  formative  activity 
of  cells  is  of  great  importance,  for  it  is  by  means 
of  this  that  wounds  heal  and  diseases  are  recovered 
from.  This  constant  destruction  and  renewal 
of  the  body  is  well  known,  and  it  is  no  doubt 
this  which  has  given  rise  to  the  belief,  widely 


DISEASE  AND   ITS  CAUSES  43 

held,  that  the  body  renews  itself  in  seven  years  and 
that  the  changes  impressed  upon  it  by  vaccina- 
tion endure  for  this  period  only.  The  truth  is 
that  the  destruction  and  renewal  of  most  tissues 
in  the  body  takes  place  in  a  much  shorter  interval, 
and,  as  we  shall  see,  this  has  nothing  to  do  with 
the  changes  concerned  in  vaccination.  All  these 
activities  of  the  cells  vary  in  different  individuals, 
in  different  parts  and  at  different  ages. 

The  lesions  or  injuries  of  the  body  which  form 
so  prominent  a  part  of  disease  vary  in  kind, 
degree  and  situation,  depending  upon  the  char- 
acter of  the  injurious  agent,  the  duration  of  its 
action  and  the  character  of  the  tissue  affected. 
The  most  obvious  injuries  are  those  produced 
by  violence.  By  a  cut,  blood  vessels  are  severed, 
the  relations  of  tissues  disturbed,  and  at  the 
gaping  edges  of  the  wound  the  tissue  usually 
protected  by  the  skin  is  exposed  to  the  air,  re- 
sulting in  destruction  of  the  cells  contained  in 
a  thin  layer  of  the  surface.  The  discoloration 
and  swelling  of  the  skin  following  a  blow  is  due 
to  rupture  of  vessels  and  escape  of  blood  and 
fluid,  and  further  injury  may  result  from  the 
interruption  of  the  circulation. 

By  the  application  of  heat  the  tissue  may  be 
charred  and  the  albumen  of  the  blood  and  tissue 
fluids  coagulated.  Living  cells  are  very  sus- 
ceptible to  the  action  of  heat,  a  temperature 
of  130  degrees  being  the  thermal  death  point, 


44         DISEASE  AND   ITS  CAUSES 

and  even  lower  temperatures  are  fatal  when  their 
action  is  prolonged.  The  action  of  the  heat  may 
produce  definite  coagulation  of  the  fluid  wathin 
the  cells  in  the  same  way  that  the  white  of  an 
egg  is  coagulated.  Certain  of  the  albumens 
of  the  body  coagulate  at  a  much  lower  tem- 
perature than  the  white  of  the  egg  (as  the 
myosin,  one  of  the  albumens  of  the  muscle  which 
coagulates  at  115°  F.,  egg  white  coagulating  at 
158°  F.),  and  in  addition  to  such  coagulation  or 
without  it  the  ferments  within  the  cell  and  to  the 
action  of  which  cellular  activity  is  due  may  be 
destroyed. 

In  diseases  due  to  parasites,  the  parasite  pro- 
duces a  change  in  the  tissue  in  its  immediate 
vicinity  often  so  great  as  to  result  in  the  death 
of  the  cells.  The  most  general  direct  cause  of 
lesions  is  toxic  or  poisonous  substances,  either 
introduced  from  without  or  formed  in  the  body. 
In  the  case  of  the  parasitic  diseases  the  mere 
presence  of  the  parasite  in  the  body  produces 
little  or  no  harm,  the  injury  being  caused  by 
poisons  which  it  produces,  and  which  act  both 
locally  in  the  vicinity  of  the  parasite  and  at  a 
distance,  being  absorbed  and  entering  the  blood 
stream.  How  certain  of  the  poisonous  substances 
act  is  easy  to  see.  Strong  caustics  act  by  coagu- 
lating the  albumen,  or  by  the  withdrawal  of 
water  from  the  cell.  Other  poisons  act  by  form- 
ing   stable    chemical    compounds    with    certain 


DISEASE  AND   ITS  CAUSES  45 

of  the  cell  constituents  and  thereby  preventing 
the  usual  chemical  processes  from  taking  place. 
Death  from  the  inhalation  of  illuminating  gas 
is  due  to  the  carbon  monoxide  contained  in  this, 
forming  a  firm  chemical  union  with  the  haemo- 
globin of  the  red  corpuscles  so  that  the  function 
of  these  as  oxygen  carriers  is  stopped. 

In  order  that  most  poisons  may  act,  it  is  es- 
sential that  they  enter  into  the  cell,  and  they 
cannot  do  this  unless  they  are  able  to  combine 
chemically  with  certain  of  the  cell  constituents. 
To  this  is  due  the  selective  action  of  -  many 
poisons.  Morphine,  for  example,  acts  chiefly 
on  tile  cells  of  the  brain;  strychnine  acts  on 
the  cells  of  the  spinal  cord  which  excite  mo- 
tion and  thus  causes  the  characteristic  muscular 
spasm.  The  poisonous  substances  produced  by 
bacteria,  as  in  the  case  of  diphtheria,  act  on  cer- 
tain of  the  organs  only.  Different  animal  species 
owe  their  immunity  to  certain  poisons  to  their 
cells  being  so  constituted  that  a  poison  cannot 
gain  entrance  into  them;  pigeons,  for  example, 
cannot  be  poisoned  by  morphia.  Individual  varia- 
tions play  an  important  part  also;  thus,  shell- 
fish are  poisonous  for  certain  individuals  and  not 
so  for  others.  Owing  to  the  variability  of  living 
structures  a  substance  may  be  poisonous  at  one 
time  and  not  at  another,  as  the  following  example 
shows.  A  man,  very  fond  of  crab  meat,  was  once 
violently  poisoned  after  eating  crabs,  being  at  that 


46         DISEASE  AND   ITS  CAUSES 

time  seemingly  in  his  usual  state  of  health,  and 
no  illness  resulted  in  others  who  had  partaken  of 
the  same  crabs.  Two  months  later  a  hearty  meal 
of  crabs  produced  no  ill  result.  There  are  also 
individuals  so  constituted  that  so  simple  a  food  as 
the  egg  is  for  them  an  active  poison. 

The  lesions  produced  by  the  action  of  injurious 
conditions  are  usually  so  distinctive  in  situation 
and  character  that  by  the  examination  of  the 
body  after  death  the  cause  of  death  can  be  ascer- 
tained. The  lesions  of  diseases  may  be  very 
obvious  to  the  naked  eye,  or  in  other  cases 
only  the  most  careful  microscopic  examination 
can  detect  even  the  presence  of  alterations.  In 
the  case  of  poisons  the  capacity  of  the  cell  for 
adaptation  to  unusual  conditions  is  of  great 
importance.  It  is  probable  that  certain  changes 
take  place  within  the  cells,  owing  to  which  the 
function  can  be  continued  in  spite  of  the  unusual 
conditions  which  the  presence  of  the  poison 
brings  about.  It  is  in  this  way  that  the  habitual 
use  of  such  poisons  as  morphine,  alcohol  and 
tobacco,  to  speak  only  of  those  best  known,  is 
tolerated.  The  cell  life  can  become  so  accustomed 
to  the  presence  of  poisons  that  the  cell  activities 
may  suffer  in  their  absence. 

Repair  of  the  injuries  which  the  body  receives 
is  effected  in  a  variety  of  ways.  We  do  not  know 
how  intracellular  repair  takes  place,  but  most 
probably  the  cells  get  rid  of  the  injured  areas 


DISEASE  AND   ITS   CAUSES  47 

either  by  ejecting  them,  or  chemical  changes  are 
produced  in  the  altered  cell  substance  breaking 
up  and  recombining  the  molecules.  When  single 
cells  are  destroyed,  the  loss  is  made  good  by  new 
formation  of  cells,  the  cell  loss  stimulating  the 
formative  activity  of  the  cells  in  the  vicinity. 
The  body  maintains  a  cell  and  tissue  equilibrium, 
and  a  loss  is  in  most  cases  repaired.  The  blood 
fluid  lost  in  a  haemorrhage  is  quickly  restored 
by  a  withdrawal  of  the  fluid  from  the  tissues  into 
the  blood,  but  the  cells  lost  are  restored  by  new 
formation  of  cells  in  the  blood-forming  organs. 
The  blood  cells  are  all  formed  in  bone  marrow  and 
in  the  lymph  nodes,  and  not  from  the  cells  which 
circulate  in  the  blood,  and  the  stimulus  to  new 
cell  formation  which  the  loss  of  blood  brings 
about  affects  this  remote  tissue. 

In  general,  repair  takes  place  most  easily  in 
tissues  of  a  simple  character,  and  where  there 
is  the  least  differentiation  of  cell  structure  for 
the  purposes  of  function.  A  high  degree  of  func- 
tion in  which  the  cell  produces  material  of  a 
complex  character  necessitates  a  complex  chemi- 
cal apparatus  to  carry  this  out,  and  a  complicated 
mechanism  is  formed  less  easily  than  a  simple 
one.  In  certain  tissues  the  cells  have  become 
so  highly  differentiated  that  all  formative  activity 
is  lost.  Such  is  the  case  in  the  nerve  cells  of  the 
brain  and  spinal  cord,  a  loss  in  which  tissue  is 
never  repaired  by  the  formation  of  new  cells; 


48         DISEASE  AND   ITS   CAUSES 

and  in  the  muscles  the  same  is  true.  The  least 
differentiation  is  seen  in  those  cells  which  serve 
the  purpose  of  mechanical  protection  only,  as 
the  cells  of  the  skin,  and  in  these  the  formative 
activity  is  very  great.  Not  only  must  the  usual 
loss  be  supplied,  but  we  are  all  conscious  of  slight 
injuries  of  the  surface  which  are  quickly  repaired. 

Repair,  other  things  being  equal,  takes  place 
more  easily  in  the  young  than  in  the  old.  New 
formation  of  cells  goes  on  with  great  rapidity 
in  intra-uterine  life,  the  child,  beginning  its  exist- 
ence as  a  single  cell  one  two  hundred  and  fiftieth 
of  an  inch  in  diameter,  attains  in  nine  months 
a  weight  of  seven  pounds.  The  only  similar 
rapidity  of  cell  formation  is  seen  in  certain  tumors; 
although  the  body  may  add  a  greater  amount 
of  weight  and  in  a  shorter  time,  by  deposit  of  fat, 
this  in  but  slight  measure  represents  a  new  forma- 
tion of  tissue,  but  is  merely  a  storage  of  food 
material  in  cells.  The  remarkable  repair  and 
even  the  new  formation  of  entire  parts  of  the 
body  in  the  tadpole  will  not  take  place  in  the 
completely  developed  frog. 

Repair  will  also  take  place  the  more  readily 
the  less  complicated  is  the  architectural  structure 
of  the  part  affected.  When  a  series  of  tissues 
variously  and  closely  related  to  one  another 
enter  into  the  structure  of  an  organ,  there  may 
be  new  formation  of  cells;  but  when  the  loss  in- 
volves more  than  this,  the  complicated  architec- 


DISEASE  AND   ITS   CAUSES  49 

tural  structure  will  not  be  completely  replaced. 
A  brick  which  has  been  knocked  out  of  a  building 
can  be  easily  replaced,  but  the  renewal  of  an  area 
of  the  wall  is  more  difficult.  In  the  kidney,  for 
example,  the  destruction  of  single  cells  is  quickly 
made  good  by  new  cell  formation,  but  the  loss 
of  an  area  of  tissue  is  never  restored.  In  the  liver, 
on  the  other  hand,  which  is  of  much  simpler 
construction,  large  areas  of  tissue  can  be  newly 
formed.  For  the  formation  of  new  cells  in  a  part 
there  must  be  a  suflficient  amount  of  formative 
material;  then  the  circulation  of  the  blood  be- 
comes more  active,  more  blood  being  brought  to 
the  part  by  dilatation  of  the  vessels  supplying  it. 
Repair  after  a  loss  can  be  perfect  or  imperfect. 
The  tissue  lost  can  be  restored  so  perfectly  that 
no  trace  of  an  injury  remains;  but  when  the 
loss  has  been  extensive,  and  in  a  tissue  of  complex 
structure,  complete  restoration  does  not  take 
place  and  a  less  perfect  tissue  is  formed  which 
is  called  a  scar.  Examination  of  the  skin  in 
almost  anyone  will  show  some  such  scars  which 
have  resulted  from  wounds.  They  are  also  found 
in  the  internal  organs  of  the  body  as  the  result 
of  injuries  which  have  healed.  The  scar  repre- 
sents a  very  imperfect  repair.  In  the  skin,  for 
example,  the  scar  tissue  never  contains  such 
complicated  apparatus  as  hair  and  sweat  glands; 
the  white  area  is  composed  of  an  imperfectly 
vascularized  fibrous  tissue  which  is  covered  with 


50         DISEASE  AND  ITS  CAUSES 

a  modified  epidermis.  The  sear  is  less  resistant 
than  the  normal  tissue,  injury  takes  place  more 
easily  in  it  and  heals  with  more  difficulty. 

Loss  brought  about  by  the  injuries  of  disease 
can  be  compensated  for,  even  when  the  healing 
is  imperfect,  by  increased  function  of  similar 
tissue  in  the  body.  There  always  seems  to  be 
in  the  body  under  the  usual  conditions  a  reserve 
force,  no  tissue  being  worked  to  its  full  capa- 
city. Meltzer  has  compared  the  reserve  force  of 
the  body  to  the  factor  of  safety  in  mechanical 
construction.  A  bridge  is  constructed  to  sus- 
tain the  weight  of  the  usual  traffic,  but  is  in 
addition  given  strength  to  meet  unusual  and 
unforeseen  demands.  The  stomach  provides 
secretion  to  meet  the  usual  demands  of  digestion, 
but  can  take  care  of  an  unusual  amount  of  food. 
The  work  of  the  heart  may  be  doubled  by  severe 
exertions,  and  it  meets  this  demand  by  increased 
force  and  rapidity  of  contraction;  and  the  same 
is  true  of  the  muscles  attached  to  the  skeleton. 
The  constant  exercise  of  this  reserve  force  breaks 
down  the  adjustment.  If  the  weight  of  the  traffic 
over  the  bridge  be  constantly  all  that  it  can 
carry,  there  quickly  comes  a  time  when  some 
slight  and  unforeseen  increase  of  weight  brings 
disaster.  The  conditions  in  the  body  are  rather 
better  than  in  the  case  of  the  bridge,  because 
with  the  increased  demand  for  activity  the 
heart,  for  example,  becomes  larger  and  stronger, 


DISEASE  AND   ITS   CAUSES         51 

and  reserve  force  rises  with  the  load  to  be  carried, 
but  the  ratio  of  reserve  force  is  diminished. 

This  discussion  of  injury  and  repair  leads  to 
the  question  of  old  age.  Old  age,  as  such,  should 
not  be  discussed  in  a  book  on  disease,  for  it  is 
not  a  disease;  it  is  just  as  natural  to  grow  old 
and  to  die  as  it  is  to  be  born.  Disease,  however, 
differs  in  many  respects  in  the  old  as  compared 
with  the  young  and  renders  some  discussion  of 
the  condition  necessary.  Changes  are  constantly 
taking  place  in  the  body  with  the  advance  of 
years,  and  in  the  embryo  with  the  advance  of 
days.  In  every  period  of  life  in  the  child,  in  the 
adult,  in  the  middle-aged  and  in  the  old  we  meet 
with  conditions  which  were  not  present  at  earlier 
periods.  There  is  no  definite  period  at  which 
the  changes  which  we  are  accustomed  to  regard 
as  those  of  old  age  begin.  This  is  true  of  both 
the  external  appearances  of  age  and  the  internal 
changes.  One  individual  may  be  fully  as  old, 
as  far  as  is  indicated  by  the  changes  of  age,  at 
fifty  as  another  at  eighty. 

With  advancing  age  certain  organs  of  the 
body  atrophy;  they  become  diminished  in  size, 
and  the  microscopic  examination  shows  absence 
or  diminished  numbers  of  the  cells  which  are 
peculiar  to  them.  The  most  striking  example 
of  this  is  seen  in  the  sexual  glands  of  females, 
and,  to  a  less  degree,  in  those  of  the  male.  There 
is  a  small  mass  or  glandular  tissue  at  the  root 


52         DISEASE  AND   ITS   CAUSES 

of  the  neck,  the  thymus,  which  gradually  grows 
from  birth  and  reaches  its  greatest  size  at  the 
age  of  fifteen,  when  it  begins  slowly  to  atrophy 
and  almost  disappears  at  the  age  of  forty.  This 
is  the  gland  which  in  the  calf  is  known  as  the 
sweetbread  and  is  a  delicious  and  valued  article 
of  food.  The  tonsils,  which  in  the  child  may  be 
so  large  as  to  interfere  with  breathing  and  swallow- 
ing, have  almost  disappeared  in  the  adult;  and 
there  are  other  such  examples. 

In  age  atrophy  is  a  prominent  change.  It  is 
seen  in  the  loss  of  the  teeth,  in  the  whitening 
and  loss  of  the  hair,  in  the  thinning  of  the  skin 
so  that  it  more  easily  wrinkles,  in  the  thinning 
and  weakening  of  the  muscles  so  that  there  is 
not  only  diminished  force  of  muscular  contrac- 
tion, but  weakening  of  the  muscles  of  support. 
The  back  curves  from  the  action  of  gravity, 
the  strength  of  the  support  of  the  muscles  at  the 
back  not  counteracting  the  pull  of  the  weight 
of  the  abdominal  viscera  in  front.  The  bones 
become  more  porous  and  more  brittle. 

The  effect  of  atrophy  is  also  seen  in  the  dim- 
inution of  all  functions,  and  in  loss  of  weight  in 
individual  organs.  That  the  brain  shares  in  the 
general  atrophy  is  evident  both  anatomically  and 
in  function.  Mental  activity  is  more  sluggish, 
impressions  are  received  with  more  difficulty, 
their  accuracy  may  be  impaired  by  accompany- 
ing changes  in  the  sense  organs,  and  the  con- 


DISEASE  AND   ITS   CAUSES  53 

cepts  formed  from  the  impressions  may  differ 
from  the  usual.  The  slowness  of  mental  action 
and  the  diminution  in  the  range  of  mental  ac- 
tivity excited  by  impressions,  and  the  slowness 
of  expression,  may  give  a  false  idea  of  the  value 
of  the  judgment  expressed.  The  expression 
changes,  the  face  becomes  more  impassive 
because  the  facial  muscles  no  longer  reflect 
the  constant  and  ever  changing  impressions 
which  the  youthful  sense  organs  convey 
to  a  youthful  and  active  brain.  That  the 
young  should  ape  the  old,  should  seek  to 
acquire  the  gravity  of  demeanor,  to  restrain  the 
quick  impulse,  is  not  of  advantage.  Loss  of 
weight  of  the  body  as  a  whole  is  not  so  appar- 
ent, there  being  a  tendency  to  fat  formation 
owing  to  the  non-use  of  fat  or  fat-forming  material 
which  is  taken  into  the  body.  One  of  the  most 
evident  alterations  is  a  general  diminution  in 
the  fluid  of  the  tissues,  to  which  is  chiefly  due  the 
lack  of  plumpness,  the  wrinkles  of  age.  The 
facial  appearance  of  age  is  given  to  an  infant 
when,  in  consequence  of  a  long-continued  diar- 
rhoea, the  tissues  become  drained  of  fluid.  Every 
market-man  knows  that  an  old  animal  is  not  so 
available  for  food,  the  tissues  are  tougher,  more 
fibrous,  not  so  easily  disintegrated  by  chewing. 
This  is  due  to  a  relative  increase  in  the  connective 
tissue  which  binds  all  parts  together  and  is  repre- 
sented in  the  white  fibres  of  meat. 


54         DISEASE  AND   ITS  CAUSES 

Senile  atrophy  is  complex  in  its  causes  and 
modes  of  production.  The  atrophy  affects  dif- 
ferent organs  in  different  degree  and  shows  great 
variation  in  situation,  in  degree  and  in  progress. 
Atrophic  changes  of  the  blood  vessels  are  of 
great  importance,  for  this  affects  the  circulation 
on  which  the  nutrition  of  all  tissues  depends. 
While  there  is  undoubted  progressive  wear  of 
all  tissues,  this  becomes  most  evident  in  the  case 
of  the  blood  vessels  of  the  body.  It  is  rare  that 
arteries  which  can  be  regarded  as  in  all  respects 
normal  are  found  in  individuals  over  forty,  and 
these  changes  progress  rapidly  with  advancing 
age.  So  striking  and  constant  are  these  vascular 
changes  that  they  seem'  almost  in  themselves 
sufficient  to  explain  the  senile  changes,  and  this 
has  been  frequently  expressed  in  the  remark  that 
age  is  determined  not  by  years,  but  by  the  con- 
dition of  the  arteries.  Comparative  studies  show 
the  falsity  of  this  view,  for  animals  which  are 
but  Uttle  or  not  at  all  subject  to  arterial  disease 
show  senile  changes  of  much  the  same  character 
as  those  found  in  man. 

There  is  another  condition  which  must  be 
considered  in  a  study  of  causes  of  age.  In  the 
ordinary  course  of  life  sUght  injuries  are  con- 
stantly being  received  and  more  or  less  perfectly 
repaired.  An  infection  which  may  but  slightly 
affect  the  ordinary  well-being  of  the  individual 
may  produce   a  considerable  damage.     Excess 


DISEASE  AND  ITS  CAUSES         55 

or  deficiency  or  improper  food,  occasional  or 
continued  use  of  alcohol  and  other  poisons  may 
lead  to  very  definite  lesions.  Repair  after  injury 
is  rarely  perfect,  the  repaired  tissue  is  more  sus- 
ceptible to  injury,  and  with  advancing  age  there 
is  constant  diminution  in  the  ease  and  perfection 
of  repair.  The  effect  of  the  sum  of  all  these 
changes  becomes  operative:  a  vicious  circle  is 
established  in  which  injury  becomes  progressively 
easier  to  acquire  and  repair  constantly  less  per- 
fect. There  is  some  adjustment,  however,  in 
that  the  range  of  activities  is  diminished,  the 
environment  becomes  narrower  and  the  organism 
adapts  its  life  to  that  environment  which  makes 
the  least  demands  upon  it. 

Whether  there  is,  entirely  apart  from  all  con- 
ditions affecting  nutrition  and  the  effect  of 
injuries  which  disturb  the  usual  cell  activities, 
an  actual  senescence  of  the  cells  of  the  body  is 
uncertain.  In  the  presence  of  the  many  factors 
which  influence  the  obvious  diminution  of  cell  ac- 
tivity in  the  old,  it  is  impossible  to  say  whether 
the  loss  of  cell  activity  is  intrinsic  or  extrinsic. 
The  life  of  the  plant  cell  seems  to  be  immortal; 
it  does  not  grow  old.  Trees  die  owing  to  acci- 
dents or  because  the  tree  acquires  in  the  course  of 
its  growth  a  mass  of  tissue  in  which  there  is  little 
or  no  life,  and  which  becomes  the  prey  of  para- 
sites. The  growing  tissue  of  a  tree  is  comprised 
in  a  thin  layer  below  the  bark,  and  the  life  of  this 


56         DISEASE  AND   ITS   CAUSES 

may  seemingly  be  indefinitely  prolonged  by 
placing  it  in  a  situation  in  which  it  escapes  the 
action  of  accidental  injuries  and  decay,  as  by 
grafting  on  young  trees.  Where  the  nature  of 
the  dead  wood  is  such  that  it  is  immune  from 
parasites  and  decay,  as  in  the  case  of  the  Se- 
quoias, life  seems  to  be  indefinitely  prolonged. 
The  growing  branches  of  one  of  these  trees, 
whose  age  has  been  estimated  with  seeming 
accuracy  at  six  thousand  years,  are  just  as  fresh 
and  the  tree  produces  its  flowers  and  fruit  in 
the  same  degree  as  a  youthful  brother  of  one 
thousand  years.  Nor  does  old  age  supervene 
in  the  unicellular  organisms.  An  amoeba  assim- 
ilates, grows  and  multiplies  just  as  long  as  the 
environment  is  favorable. 

Old  age  in  itself  is  seldom  a  cause  of  death.  In 
rare  cases  in  the  very  old  a  condition  is  found  in 
which  no  change  is  present  to  which  death  can 
be  attributed,  all  organs  seem  to  share  alike  in 
the  senescence.  Death  is  usually  due  to  some 
of  the  accidents  of  life,  a  slight  infection  to  which 
the  less  resistant  body  succumbs,  or  to  the  rup- 
ture of  a  weakened  blood  vessel  in  the  brain,  or 
to  more  advanced  decay  in  some  organ  whose 
function  is  indispensable.  The  causes  and  con- 
ditions of  age  have  been  a  fertile  source  for  specu- 
lation. Many  of  the  hypotheses  have  been 
interesting,  that  of  Metschnikoff,  for  example, 
who  finds  as  a  dominating  influence  in  causing 


DISEASE  AND   ITS   CAUSES  57 

senescence  the  absorption  of  toxic  substances 
formed  in  the  large  intestine  by  certain  bacteria. 
He  further  finds  that  the  cells  of  the  body  which 
have  phagocytic  powers  turn  their  activity 
against  cells  and  tissues  which  have  become 
weakened.  There  may  be  absorption  of  injurious 
substances  from  the  intestines  which  the  body 
in  a  vigorous  condition  is  able  to  destroy  or  to 
counteract  their  influence,  and  these  may  be 
more  operative  in  the  weaker  condition  of  the 
body  in  the  old.  Phagocytes  will  remove  cells 
which  are  dead  and  often  cells  which  are  super- 
fluous in  a  part,  but  there  is  no  evidence  that 
this  is  ever  other  than  a  conservative  process. 
Since  it  is  impossible  to  single  out  any  one  con- 
dition to  which  old  age  is  due,  the  hypothesis  of 
MetschnikofI  should  have  no  more  regard  given 
it  than  the  many  other  hypotheses  which  have 
been  presented. 

Death  of  the  body  as  a  whole  takes  place  from 
the  cessation  of  the  action  of  the  central  nervous 
system  or  of  the  respiratory  system  or  of  the 
circulation.  There  are  other  organs  of  the  body, 
such  as  the  intestine,  kidney,  liver,  whose  func- 
tion is  essential  for  life,  but  death  does  not  take 
place  immediately  on  the  cessation  of  their 
function.  The  functions  of  the  heart,  the  brain 
and  the  lungs  are  intimately  associated.  Oxygen 
is  indispensable  for  the  life  of  the  tissues,  and 
its  supply  is  dependent  upon  the  integrity  of  the 


58         DISEASE  AND  ITS  CAUSES 

three  organs  mentioned,  which  have  been  called 
the  tripos  of  hfe.  Respiration  is  brought  about 
by  the  stimulation  of  certain  nerve  cells  in  the 
brain,  the  most  effective  stimulus  to  these  cells 
being  a  diminution  of  oxygen  in  the  blood  sup- 
plying them.  These  cells  send  out  impulses  to 
the  muscles  concerned  in  inspiration,  the  chest 
expands,  and  air  is  taken  into  the  lungs.  Respi- 
ration is  then  a  more  complicated  process  than 
is  the  action  of  the  heart,  for  its  contraction, 
which  causes  the  blood  to  circulate,  is  not  im- 
mediately dependent  upon  extrinsic  influences. 
Death  is  usually  more  immediately  due  to  failure 
of  respiration  than  to  failure  of  circulation,  for 
the  heart  often  continues  beating  for  a  time  after 
respiration  has  ceased.  Thus,  in  cases  of  drown- 
ing and  suffocation,  by  means  of  artificial  respi- 
ration in  which  air  is  passively  taken  into  and 
expelled  from  the  lungs,  giving  oxygen  to  the 
blood,  the  heart  may  continue  to  beat  and  the 
circulation  continue  for  hours  after  all  evident 
signs  of  life  and  all  sensation  has  ceased. 

By  this  general  death  is  meant  the  death  of 
the  organism  as  a  whole,  but  all  parts  of  the  body 
do  not  die  at  the  same  time.  The  muscles  and 
nerves  may  react,  the  heart  may  be  kept  beating, 
and  organs  of  the  body  when  removed  and  sup- 
plied with  blood  will  continue  to  function.  Cer- 
tain tissues  die  early,  and  the  first  to  succumb 
to  the  lack  of  *  oxygenated  blood  are  the  nerve 


DISEASE  AND  ITS  CAUSES         59 

cells  of  the  brain.  If  respiration  and  circulation 
have  ceased  for  as  short  a  time  as  twelve  minutes, 
life  ceases  in  certain  of  these  cells  and  cannot  be 
restored.  This  is  again  an  example  of  the  greater 
vulnerability  of  the  more  highly  differentiated 
structure  in  which  all  other  forms  of  cell  activity 
are  subordinated  to  function.  There  are,  however, 
pretty  well  authenticated  cases  of  resuscitation 
after  immersion  in  water  for  a  longer  period  than 
twelve  minutes,  but  these  cases  have  not  been 
carefully  timed,  and  time  under  such  conditions 
may  seem  longer  than  it  actually  is;  and  there 
is,  moreover,  the  possibility  of  a  slight  gaseous 
interchange  between  the  blood  and  the  water 
in  the  lungs,  as  in  the  case  of  the  fish  which  uses 
the  water  for  an  oxygen  supply  as  the  mammal 
does  the  air.  There  are  also  examples  of  apparent 
death  or  trances  which  have  lasted  longer,  and 
the  cases  of  fakirs  who  have  been  buried  for 
prolonged  periods  and  again  restored  to  life. 
In  these  conditions,  however,  all  the  activities 
of  the  body  are  reduced  to  the  utmost,  and  respi- 
ration and  circulation,  so  feeble  as  to  be  imper- 
ceptible to  ordinary  observation,  suffice  to  keep 
the  cells  living. 

With  the  cessation  of  life  the  body  is  subject 
to  the  unmodified  action  of  its  physical  environ- 
ment. There  is  no  further  production  of  heat 
and  the  body  takes  the  temperature  of  the  sur- 
roundings.    The  only  exceptions  are  rare  cases 


60         DISEASE  AND   ITS   CAUSES 

in  which  such  active  chemical  changes  take  place 
in  the  dead  body  that  heat  is  generated  by  chem- 
ical action.  At  a  varying  interval  after  death, 
usually  within  twelve  hours,  there  is  a  general 
contraction  and  hardening  of  the  muscles  due 
to  chemical  changes,  probably  of  the  nature  of 
coagulation,  in  them.  This  begins  in  the  muscles 
of  the  head,  extends  to  the  extremities,  and 
usually  disappears  in  twenty-four  hours.  It  is 
always  most  intense  and  most  rapid  in  its  onset 
when  death  is  preceded  by  active  muscular  exer- 
tion. There  have  been  cases  of  instantaneous 
death  in  battle  where  the  body  has  remained  in 
the  position  it  held  at  the  moment  of  death,  this 
being  due  to  the  instantaneous  onset  of  muscular 
rigidity.  The  blood  remains  fluid  for  a  time  after 
death  and  settles  in  the  more  dependent  parts  of 
the  body,  producing  bluish  red  mottled  discolor- 
ations.  Later  the  blood  coagulates  in  the  vessels. 
The  body  loses  moisture  by  evaporation.  Drying 
of  the  surface  takes  place  where  the  epidermis 
is  thin,  as  over  the  transparent  part  of  the  eye 
and  over  areas  deprived  of  epidermis.  Decompo- 
sition and  putrefaction  of  the  body  due  to  bac- 
terial action  takes  place.  The  bacteria  ever 
present  in  the  alimentary  canal  make  their  way 
from  this  into  the  dead  tissue.  Certain  of  these 
bacteria  produce  gas  which  accumulates  in  the 
tissues  and  the  body  often  swells  enormously. 
A  greenish  discoloration  appears,  which  is  due 


DISEASE  AND   ITS   CAUSES  61 

to  the  union  of  the  products  of  decomposition 
with  the  iron  in  the  blood;  this  is  more  promi- 
nent over  the  abdomen  and  appears  in  Hues  along 
the  course  of  the  veins.  The  rapidity  with  which 
decomposition  takes  place  varies,  and  is  dependent 
upon  many  factors,  such  as  the  surrounding 
temperature,  the  nutrition  of  the  body  at  the 
time  of  death,  the  cause  of  death.  It  is  usually 
not  diflficult  to  recognize  that  a  body  is  dead. 
In  certain  cases,  however,  the  heart's  action 
may  be  so  feeble  that  no  pulse  is  felt  at  the  wrist, 
and  the  current  of  the  expired  air  may  not  move 
a  feather  held  to  the  nostril  or  cloud  the  surface 
of  a  mirror  by  the  precipitation  of  moisture  upon 
it.  This  condition,  combined  with  unconscious- 
ness and  paralysis  of  all  the  voluntary  muscles, 
may  very  closely  simulate  death.  The  only 
absolute  evidence  of  death  is  given  by  such 
changes  as  loss  of  body  heat,  rigor  mortis  or 
stiffening  of  the  muscles,  coagulation  of  the 
blood  and  decomposition. 


CHAPTER  III 

The  Growth  of  the  Body.  —  Growth  more  Rapid  in 
Embryonic  Period.  —  The  Coordination  and  Regula- 
tion op  Growth.  —  Tumors.  —  The  Growth  of  Tumors 

COMPARED     with     NoRMAL    GrOWTH. SiZE,    ShAPE    AND 

Structure  of  Tumors.  —  The  Growth  Capacity  of 
Tumors  as  shown  by  the  Inoculation  of  Tumors 
op  Mice.  —  Benign  and  Malignant  Tumors.  —  Effect 
op  Inheritance.  —  Are  Tumors  becoming  more  Fre- 
quent ?  —  The  Effect  produced  by  a  Tumor  on  the 
Individual  who  bears  it.  —  Relation  of  Tl^mors  to 
Age  and  Sex.  —  Theories  as  to  the  Cause  of  Tumors. 

—  The  Parasitic  Theory.  —  The  Traumatic  Theory. 

—  The  Embryonic  Theory.  —  The  Importance  of  the 
Eauly  Recognition  and  Removal  op  Tumors. 

The  power  of  growth  is  possessed  by  every 
living  thing,  but  growth  is  not  limited  to  the 
living.  Crystals  also  will  grow,  and  the  rapidity 
and  character  of  growth  and  the  maximum  size 
of  the  crystal  depends  upon  the  character  of  the 
substance  which  forms  the  crystal.  From  the 
single  cell  or  ovum  formed  by  the  union  of  the 
male  and  female  sexual  cells,  growth  is  continu- 
ous until  a  size  corresponding  to  the  type  of 
the  species  is  attained.  From  this  time  onward 
growth  is  limited  to  the  degree  necessary  to  sup- 
ply the  constant  loss  of  material  which  the  body 
undergoes.  The  rapidity  of  the  growth  of  the 
body  and  of  its  component  parts  diflFers  at  differ- 
62 


DISEASE  AND   ITS  CAUSES  63 

ent  ages,  and  becomes  progressively  less  active 
from  its  beginning  in  the  ovum  until  the  adult 
type  of  the  species  is  attained.  As  determined 
by  the  volume,  the  embryo  increases  more  than 
ten  thousand  times  in  size  during  the  first  month 
of  intra-uterine  life.  At  birth  the  average  weight 
is  six  and  a  half  pounds;  at  the  end  of  the  first 
year  eighteen  and  a  half  pounds,  a  gain  of  twelve 
pounds;  at  the  end  of  the  second  year  twenty- 
three  pounds,  a  gain  of  four  and  a  half  pounds. 
The  growth  is  coordinated,  the  size  of  the  single 
organs  bearing  a  definite  ratio,  which  varies 
within  slight  limits,  to  the  size  of  the  body,  a  large 
individual  having  organs  of  corresponding  size. 
Knowing  that  the  capacity  of  growth  is  one  of 
the  inherent  properties  of  living  matter,  it  is 
much  easier  to  understand  the  continuance  of 
growth  than  its  cessation.  It  is  impossible  to 
avoid  the  conclusion  that  there  is  some  internal 
mechanism  of  the  body  which  controls  and  regu- 
lates growth.  In  the  first  chapter  reference  was 
made  to  organs  producing  substances  which  pass 
directly  into  the  circulation;  these  substances  act 
by  control  of  the  activities  of  other  parts,  stimu- 
lating or  depressing  or  altering  their  function. 
Two  of  these  glands,  the  thymus,  lying  in  front, 
where  the  neck  joins  the  body  and  which  attains 
its  greatest  size  at  puberty,  and  the  pituitary 
body,  placed  beneath  the  brain  but  forming  no 
part  of  it,  have  been  shown  by  recent  investiga- 


64         DISEASE  AND   ITS   CAUSES 

tions  to  have  a  very  definite  relation  to  growth, 
especially  the  growth  of  the  skeleton.  The 
growth  energy  chiefly  resides  in  the  skeleton, 
and  if  the  growing  animal  has  a  diet  sufficient 
only  to  maintain  the  body  weight,  the  skeleton 
will  continue  to  grow  at  the  expense  of  the  other 
tissues,  literally  living  upon  the  rest  of  the  body. 
Disease  of  the  glands  mentioned  leading  to  an 
increase  or  diminution  or  alteration  of  their  func- 
tion may  not  only  inhibit  or  unduly  increase  the 
growth  of  the  skeleton,  but  may  also  interfere 
with  the  sexual  development  which  accompanies 
the  skeleton  growth. 

The  difficulties  which  arise  in  an  endeavor  to 
comprehend  normal  growth  are  greater  when  the 
growth  of  tumors  is  considered.  A  tumor  is  a 
mass  of  newly  formed  tissue  which  in  structure, 
in  growth,  and  the  relations  which  it  forms  with 
adjoining  tissues  departs  to  a  greater  or  less 
degree  from  the  type  of  the  tissue  to  which  it 
is  related  in  structure  or  from  which  it  originates. 
It  is  an  independent  structure  which,  like  a 
parasite,  grows  at  the  expense  of  the  body, 
contributing  nothing  to  it,  and  its  capacity  for 
growth  is  unlimited.  A  tumor  cannot  be  con- 
sidered as  an  organ,  its  activities  not  being  co- 
ordinated with  those  of  the  body.  A  part  of  the 
body  it  certainly  is,  but  in  the  household  economy 
it  is  to  be  considered  as  a  wild  and  lawless  guest, 
not  influenced  by  or  conforming  with  the  regu- 


DISEASE  AND   ITS  CAUSES  65 

lations  of  the  household.  The  rapidity  of  growth 
varies;  certain  tumors  for  years  increase  but 
Uttle  in  size,  while  others  may  be  seen  to  increase 
from  day  to  day.  The  growth  is  often  intermit- 
tent, periods  of  great  activity  of  growth  alter- 
nating with  periods  of  quiescence.  The  nutrition 
and  growth  of  a  tumor  is  only  slightly  influenced 
by  the  condition  of  nutrition  of  the  bearer.  Its 
cells  have  a  greater  avidity  for  food  than  have 
those  of  the  body,  and,  like  the  growing  bones 
of  an  insufficiently  fed  animal,  growth  in  some 
cases  seems  to  take  place  at  the  expense  of  the 
body,  the  normal  cells  not  obtaining  sufficient 
nutriment  to  repair  their  waste. 

A  tumor  may  be  of  any  size:  so  small  as  to 
be  invisible  to  the  naked  eye,  or  its  weight  may 
exceed  that  of  the  individual  who  bears  it.  The 
limitations  to  its  growth  are  extrinsic  and  not 
intrinsic.  There  is  no  distinct  color.  Certain 
tumors  have  color  which  depends  upon  the 
presence  of  a  dark  brown  or  black  pigment  within 
the  cells.  Haemorrhages  within  them  are  not 
infrequent,  and  they  may  be  colored  by  the  blood 
or  by  pigments  formed  from  it.  Usually  they 
have  a  gray  color  modified  by  their  varying 
vascularity,  or  the  cut  surface  may  be  mottled 
due  to  areas  of  cell  degeneration.  The  consist- 
ency varies;  some  tumors  are  so  soft  that  they  can 
be  pressed  through  a  sieve,  others  are  of  stony 
hardness.     There  is  no  distinct  shape,  this  being 


66         DISEASE  AND  ITS  CAUSES 

influenced  by  the  nature  of  the  tumor,  the  man- 
ner of  growth  and  situation.  When  the  tumor 
grows  on  or  near  a  surface,  it  may  project  from 
this  and  be  attached  by  a  narrow  band  only;  in 
the  interior  of  the  body  it  may  be  irregular  in 
outline,  round  or  lobular,  the  shape  being  influ- 
enced by  many  factors.  Tumors  like  the  tissues 
of  the  normal  body  are  nourished  by  the  blood 
and  contain  blood  vessels  often  in  great  numbers. 

A  tumor  arises  by  the  cells  of  a  part  of  the 
body  beginning  to  grow  and  taking  on  the  charac- 
teristics of  a  tumor.  Its  growth  is  independent, 
the  cells  of  the  adjoining  tissue  taking  no  part 
in  it.  The  tissue  in  the  vicinity  of  the  tumor  is 
partly  pushed  aside  by  the  mass,  or  the  tumor 
grows  into  it  and  the  tissue  disappears  as  the 
tumor  advances.  The  destruction  of  the  sur- 
rounding tissue  is  brought  about  partly  by  the 
pressure  which  the  tumor  exerts,  partly  by  the 
compression  of  the  blood  vessels  or  the  blcod 
supply  of  the  organs  is  diverted  to  the  tumor. 

The  characteristics  of  a  tumor  are  due  to  the 
cells  which  it  contains  (Fig.  14).  These  often 
become  separated  from  the  main  mass  and  are 
carried  by  the  blood  into  other  parts  of  the  body, 
where  they  grow  and  form  tumors  similar  in 
character  to  the  parent  tumor.  In  the  extraor- 
dinary capacity  for  growth  possessed  by  tumor 
cells,  they  resemble  vegetable  rather  than  animal 
cells.    There  is  no  limit  to  the  growth  of  a  tumor 


DISEASE  AND  ITS  CAUSES 


67 


save  by  the  death  of  the  individual  who  bears 
it,  thus  cutting  off  the  supply  of  nutrition.  The 
cells  of  tumors  peculiar  to  man  show  a  narrow 
range  of  adaptation.     They  will  grow  only  in 


Fig.  14.  —  Photograph  of  a  microscopic  preparation 
FROM  A  CANCER  OF  THE  UTERUS.  A  large  mass  of  cells  is 
extending  into  the  tissue  of  the  uterus  which  is  shown  as 
the  fibrous  structure.  Such  a  cell  mass  penetrating  into  the 
tissue  represents  the  real  cancer,  the  tissue  about  the  cell 
masses  bear  the  blood  vessels  which  nourish  the  tumor  cells. 

the  body  of  the  individual  to  whom  the  tumor 
belongs,  and  die  when  grafted  on  another  indi- 
vidual. In  the  case  of  tumors  which  arise  in 
animals,  pieces  of  the  tumor  when   grafted  on 


68         DISEASE  AND   ITS  CAUSES 

another  animal  of  the  same  species  will  grow,  and 
in  this  way  the  growth  capacity  of  the  tumor 
cells  has  been  estimated.  Thus,  by  transplanting 
a  small  section  of  a  mouse  tumor  into  other  mice, 
the  small  transplanted  fragments  will  in  two 
weeks  grow  to  the  size  of  filberts,  and  each  of 
these  will  furnish  material  to  engraft  upon  ten 
mice.  These  new  tumors  are  similar  in  character 
to  the  original  tumor,  and  really  represent  parts 
of  it  in  the  same  way  that  all  the  Baldwin  apples 
in  the  world  are  parts  of  the  original  tree  which 
was  found  in  Baldwinville  many  years  ago,  and 
as  all  the  Concord  grape  vines  are  really  parts  of 
the  original  vine.  It  has  been  estimated  that 
if  all  the  growth  capacity  of  this  mouse  tumor 
were  availed  of  by  the  successive  inoculation  of 
other  mice,  a  mass  of  tumor  several  times  the 
diameter  of  the  sun  would  grow  in  two  years. 
The  condition  of  the  individual  seems  to  exert 
no  influence  upon  the  growth  of  the  tumor. 
Growth  may  be  as  rapid  when  the  bearer  is  in 
a  condition  of  extreme  emaciation  as  it  is  when 
the  bearer  is  well  nourished  and  robust. 

Those  tumors  which  grow  rapidly  and  invade 
and  destroy  the  surrounding  tissue  are  called 
malignant  tumors  or  cancers,  but  in  a  strict  sense 
no  tumor  can  be  regarded  as  benign,  for  none 
can  serve  a  useful  purpose.  A  tumor  after  a 
period  of  slow  growth  can  begin  to  grow  rapidly. 
Tumors  may  arise  in  any  part  of  the  body,  but 


DISEASE  AND   ITS   CAUSES  69 

there  are  certain  places  of  preference  particu- 
larly for  the  more  malignant  tumors.  These 
are  places  where  the  cells  naturally  have  a  marked 
power  of  growth,  and  especially  where  growth  is 
intermittent  as  in  the  uterus  and  mammary 
gland. 

Little  is  known  in  regard  to  the  influence  of 
inheritance  on  the  formation  of  tumors.  Study 
of  the  tumors  of  mice  show  a  slightly  greater 
susceptibility  to  tumor  formation  in  the  progeny 
of  mice  who  have  developed  tumors.  Studies 
of  human  families  seem  to  show  that  heredity 
has  a  slight  influence,  but  in  the  frequency  of 
tumors  such  statistical  evidence  is  of  little  value. 
The  question  of  inheritance  has  much  bearing 
on  the  origin  of  tumors.  If  the  tumor  is  accidental 
and  due  entirely  to  extraneous  causes,  inheritance 
is  not  probable;  but  if  there  is  some  predisposi- 
tion to  tumor  formation  in  certain  individuals  due 
to  some  peculiarity,  then  inheritance  may  exert 
an  influence. 

The  question  as  to  whether  tumors  are  an 
increasing  cause  of  disease  is  equally  difficult 
of  solution.  The  mortality  statistics,  if  taken 
at  their  face  value,  show  an  enormous  increase 
in  frequency;  but  there  are  many  factors  which 
must  be  considered  and  which  render  the  decision 
difficult  and  doubtful.  Tumors  are  largely  a 
prerogative  of  age,  and  the  increased  duration 
of  life  which  preventive  medicine  has  brought 


70         DISEASE  AND  ITS  CAUSES 

about  brings  more  people  into  the  age  when 
tumors  are  more  common.  Owing  to  the  greater 
skill  in  the  diagnosis  of  tumors,  especially  those 
of  the  internal  organs,  they  are  now  recognized 
more  frequently  and  more  deaths  are  correctly 
ascribed  to  them.  Deaths  from  tumors  were 
formerly  often  purposely  concealed  and  attributed 
to  some  other  cause. 

No  age  is  immune  to  tumors.  They  may  be 
present  at  birth  or  develop  shortly  afterwards. 
The  age  from  five  to  twenty  years  is  the  most 
free  from  them,  that  from  forty-five  to  sixty-five 
the  most  susceptible,  particularly  to  the  more 
malignant  forms. 

A  tumor  is  a  local  disease.  The  growing  tis- 
sue of  the  tumor  is  the  disease,  and  it  is  evident 
that  if  the  entire  tumor  were  removed  the  disease 
would  be  cured.  This  is  the  end  sought  by  surgi- 
cal interference,  but  notwithstanding  seemingly 
thorough  removal,  the  tumor  often  reappears 
after  an  interval  of  months  or  years.  There  are 
many  conditions  which  may  render  the  complete 
removal  of  a  tumor  diflScult  or  impossible.  It 
is  often  impossible  to  ascertain  just  how  far  the 
tumor  cells  have  invaded  the  neighboring  struc- 
tures; the  situation  of  the  tumor  may  be  such 
that  an  extended  removal  would  injure  organs 
which  are  essential  for  life,  or  at  the  time  of 
removal  the  tumor  cells  may  have  been  conveyed 
elsewhere   by   the  blood   or  lymphatic   vessels. 


DISEASE  AND  ITS  CAUSES         71 

Successful  removal  depends  mainly  upon  the 
length  of  time  the  tumor  has  been  growing.  At 
an  early  stage  even  the  most  malignant  tumo^ 
may  be  successfully  removed.  It  is  evident 
from  this  how  disastrous  may  be  the  neglect 
of  proper  surgical  treatment  of  a  tumor.  The 
time  may  be  very  short  between  the  first  evi- 
dence of  the  presence  of  a  tumor  and  the  develop- 
ment of  a  condition  which  would  render  complete 
removal  impossible. 

The  effect  of  a  tumor  upon  its  bearer  depends 
upon  its  character  and  situation.  Pain  is  very 
commonly  present,  and  is  due  to  the  pressure 
which  the  growing  tumor  exerts  upon  the  sensory 
nerves.  Pain  may,  however,  not  be  present  or 
appear  only  at  the  last.  A  condition  of  mal- 
nutrition and  emaciation  often  results  due  to 
the  passage  into  the  blood  of  injurious  substances 
formed  in  the  tumor,  or  to  the  destruction  of 
important  organs  by  the  growing  tumor.  The 
growth  of  a  tumor  in  the  intestine  may  obstruct 
or  close  the  canal  and  thus  interfere  with  nutrition. 

The  cause  or  causes  of  tumors  are  unknown. 
We  know  that  the  tumor  represents  essentially 
an  abnormal  growth,  and  that  this  growth  is  due 
to  new  formation  of  cells.  In  certain  cases  the 
tumor  repeats  the  structure  of  the  organ  or  tissue 
in  which  it  originates,  in  others  it  departs  widely 
from  this;  always,  however,  its  structure  re- 
sembles structures  found  in  the  body  at  some 


72         DISEASE  AND   ITS  CAUSES 

period  of  life.  The  tumor  cells,  like  all  other 
cells  of  the  body,  grow  by  means  of  the  nutriment 
which  the  body  supplies;  they  have  no  intrinsic 
sources  of  energy.  The  great  problem  is  what 
starts  the  cells  to  grow  and  why  the  growth 
differs  from  that  of  normal  tissue,  why  it  is 
not  regulated  and  coordinated  as  are  other 
forms  of  growth.  When  a  small  piece  of  the 
skin,  for  instance,  is  cut  out  growth  as  rapid  as 
that  in  tumors  takes  place  in  the  adjoining  cells, 
but  it  ceases  when  the  loss  is  restored.  The  same 
is  true  when  a  piece  of  the  hver  is  removed. 

Various  hypotheses  have  been  formed  to  ex- 
plain the  tumor,  all  of  them  of  interest,  and  they 
have  had  great  importance  in  that  the  attempt 
to  prove  or  disprove  the  hypothesis  by  continued 
observation  and  experiment  along  definite  lines 
has  produced  new  knowledge.  The  various 
theories  as  to  cause  may  be  divided  into  three 
heads. 

The  parasitic  theory.  This  supposes  that  a 
living  parasite  invades  the  body,  and  by  its 
presence  excites  the  cells  of  certain  tissues  to 
grow  in  tumor  form.  It  is  known  that  active 
growth  of  the  cells  of  the  body  can  be  excited  in 
a  number  of  ways,  by  chemical  substances  such 
as  certain  of  the  coal  tar  products,  and  that  it 
often  takes  place  under  the  influence  of  bacteria. 
It  is  further  known  that  parasites  can  produce 
tumor-like  growths  in  plants.    The  large,  rough 


DISEASE  AND   ITS   CAUSES  73 

excrescences  on  the  oaks  are  produced  by  a  fly 
which  lays  its  eggs  in  or  beneath  the  bark,  and 
the  larva  which  develops  from  the  egg  secretes 
a  substance  which  causes  the  cells  about  it  to 
multiply,  and  a  huge  mass  is  formed  which  serves 
the  developing  insect  for  both  food  and  pro- 
tection. Large  tumor-like  masses  are  formed  on 
the  roots  and  stalk  of  cabbages  as  the  result  of 
the  invasion  of  the  cells  by  a  minute  organ- 
ism: the  tumors  of  olive  trees  are  due  to  a  bac- 
terium; the  peculiar  growths  on  cedar  trees,  the 
so-called  "witches'  brooms, "are  produced  by  a 
fungus,  and  there  are  many  other  such  examples. 
These  have  many  analogies  with  tumors  in  ani- 
mals. Under  the  stimulus  of  the  parasite  the 
cells  seem  to  have  unlimited  growth  capacity 
and  a  greater  nutritive  avidity  than  have  the 
normal  plant  cells;  the  character  of  the  mass 
produced  differs  as  does  the  tumor,  to  a  greater 
or  less  extent,  from  the  normal  growth;  on  the 
cedar,  for  instance,  the  "witches'  broom"  con- 
sists of  a  thick  mass  of  foliage  with  small  stems 
less  green  than  the  usual  foliage,  the  leaves  wider 
and  not  so  closely  applied  to  the  stems.  The 
entire  plant  suffers  in  its  nutrition  and  a  condition 
resembling  tumor  cachexia^  is  produced,  and  there 
are  no  fundamental  differences  between  the  plant 

'  By  cachexia  is  understood  a  condition  of  malnutrition 
and  emaciation  which  is  usually  accompanied  by  a  pale  sallow 
color  of  the  skin. 


74         DISEASE  AND  ITS  CAUSES 

and  animal  tumors.  Support  has  also  been 
given  to  the  parasitic  theory  by  the  discovery 
within  tumor  cells  of  bodies  which  were  supposed 
to  be  a  peculiar  sort  of  parasite.  If  the  truth 
of  the  parasitic  theory  could  be  proved,  there 
would  be  justifiable  expectation  that  the  tumor 
disease  might  be  controlled  as  are  many  of  the 
parasitic  diseases,  but  the  hypothesis  awaits  the 
demonstration  of  its  correctness.  Despite  the 
study  of  tumors  which  is  being  actively  pursued 
in  many  places  and  by  the  most  skilled  investi- 
gators, no  parasites  have  been  found  in  animal 
tumors;  the  objects  previously  described  as  par- 
asites have  been  found  not  to  be  such.  It  is 
difficult  to  bring  in  accord  with  the  parasitic 
theory  the  great  variation  in  tumor  struc- 
ture, the  relation  of  certain  tumors,  as  the 
mahgnant  tumors  of  the  breast  and  uterus, 
with  the  age  of  the  bearer,  the  congenital 
tumors  which  develop  in  intra-uterine  life,  and 
there  are  many  other  conditions  which  oppose 
the  theory. 

The  traumatic  ^  theory.  There  is  much  in 
favor  of  this.  In  a  certain  number  of  cases 
tumors  do  develop  at  the  site  of  injuries.  The 
coincidence  of  injury  and  tumor  is  apt  to  be 
overestimated  because  of  the  strong  tendency 
to  connect  succeeding  events.  Tumors  are  not 
most  common  on  those  parts  of  the  body  which 

^  By  trauma  is  understood  a  wound  or  injury  of  any  sort. 


DISEASE  AND   ITS  CAUSES  75 

are  most  exposed  to  injury.  They  are  rare,  for 
instance,  on  the  hands  and  feet,  and  very  rarely 
do  they  appear  at  the  site  of  wounds  caused  by 
surgical  operations.  For  those  tumors  which 
develop  in  intra-uterine  life  it  is  difficult  to  as- 
sign injury  as  a  cause.  There  does,  however,  seem 
to  be  a  relation  between  tumors  and  injuries  of 
a  certain  character.  The  natives  of  Cashmere 
use  in  winter  for  purposes  of  heat  a  small  char- 
coal stove  which  they  bind  on  the  front  of  the 
body;  bums  often  result  and  tumors  not  in- 
frequently develop  at  the  site  of  such  burns. 
Injuries  of  tissue  which  are  produced  by  the 
X-ray  not  infrequently  result  in  tumor  formation 
and  years  may  elapse  between  the  receipt  of  the 
injury  and  the  development  of  the  tumor.  These 
X-ray  injuries  are  of  a  peculiar  character,  their 
nature  but  imperfectly  understood,  and  the  in- 
jured tissues  seem  to  have  lost  the  capacity  for 
perfect  repair. 

In  regard  to  the  possible  action  of  both  in- 
juries and  parasites  in  causing  tumors,  the  possi- 
bility that  their  effects  on  different  individuals 
may  not  be  the  same  must  be  considered.  In 
addition  to  the  trauma  or  the  parasite  which  may 
be  considered  as  extrinsic  factors,  there  may  be 
conditions  of  the  body,  intrinsic  factors,  which 
favor  their  action  in  tumor  development.  The 
peculiar  tissue  growth  within  the  uterus  called 
decidua,  which   occurs    normally  in   pregnancy 


76  DISEASE  AND   ITS  CAUSES 

and  serves  to  fasten  the  developing  ovum  to 
the  inner  lining  of  the  uterus,  may  be  pro- 
duced experimentally.  This  growth  depends 
upon  two  factors,  an  internal  secretion  derived 
from  the  ovary  and  the  introduction  into  the 
uterus  of  a  foreign  body  of  some  sort ;  in 
the  case  of  pregnancy  the  developing  embryo 
acts  as  the  foreign  body.  It  is  not  impos- 
sible that  some  variation  in  the  complex  rela- 
tions which  determine  normal  growth  may  be 
one  factor,  possibly  the  most  important,  in  tumor 
formation. 

Another  theory  is  that  the  tumor  is  the  result 
of  imperfect  embryonic  development.  The  devel- 
opment of  the  child  from  the  ovum  is  the  result 
of  a  continued  formation  and  differentiation  of 
cells.  A  cell  mass  is  first  produced,  and  the  cells 
in  this  diflFerentiate  into  three  layers  called 
ectoderm,  entoderm  and  mesoderm,  from  which 
the  external  and  internal  surfaces  and  the  en- 
closed tissues  respectively  develop,  and  the 
different  organs  are  produced  by  growth  of  the 
cells  of  certain  areas  of  these  layers.  The  em- 
bryonic theory  assumes  that  in  the  course  of 
embryonic  development  not  all  the  cell  material 
destined  for  the  formation  of  individual  organs 
is  used  up  for  this  purpose,  that  certain  of  the 
embryonic  cells  become  enclosed  in  the  develop- 
ing organs,  they  retain  the  embryonic  capacity 
for  growth  and  tumors  arise  from  them.     There 


DISEASE  AND   ITS  CAUSES  77 

is  no  doubt  that  something  Hke  this  does  take 
place.  There  is  a  relation  between  malformations 
due  to  imperfect  development  of  the  embryo  and 
tumors,  the  two  conditions  occurring  together  too 
frequently  to  be  regarded  as  mere  coincidence. 
Also  tumors  may  occur  in  parts  of  the  body  in 
which  there  is  no  tissue  capable  of  forming  struc- 
tures which  may  be  present  in  the  tumors.  The 
theory,  however,  is  not  adequate,  but  it  may 
be  among  the  factors. 

The  problems  concerned  in  the  nature  and 
cause  of  tumors  are  the  most  important  in  medi- 
cine at  the  present  time.  No  other  form  of 
disease  causes  a  similar  amount  of  suffering  and 
anxiety,  which  often  extends  over  years  and  makes 
a  terrible  drain  on  the  sympathy  and  resources 
of  the  family.  The  only  efficient  treatment  for 
tumors  at  the  present  time  is  removal  by  surgical 
operation,  and  the  success  of  the  operation  is  in 
direct  ratio  to  the  age  of  the  tumor,  the  time 
which  elapses  from  its  beginning  development. 
It  is  of  the  utmost  importance  that  this  should 
be  generally  recognized,  and  the  facts  relating 
to  tumors  become  general  knowledge.  Tumors 
form  one  of  the  most  common  causes  of  death 
(after  the  age  of  thirty-five  one  in  every  ten 
individuals  dies  of  tumor);  medical  and  surgical 
resources  are,  in  many  cases,  powerless  to  afford 
relief  and  the  tumor  stands  as  a  bar  to  the  at- 
tainment of  the  Utopia  represented  by  a  happy 


78         DISEASE  AND   ITS  CAUSES 

and  comfortable  old  age,  and  a  quiet  passing. 
Every  possible  resource  should  be  placed  at  the 
disposal  of  the  scientific  investigation  of  the 
subject,  for  with  knowledge  will  come  power  to 
relieve. 


CHAPTER  IV 

The  Reactions  op  the  Tissues  op  the  Body  to  In- 
juries. —  Inflammation.  —  The  Changes  in  the  Blood 
IN  this.  —  The  Emigration  of  the  Corpuscles  of  the 
Blood. — The  Evident  Changes  in  the  Injured  Part 
AND  THE  Manner  in  which  these  are  produced.  — 
Heat,  Redness,  Swelling  and  Pain.  —  The  Produc- 
tion op  Blisters  by  Sunburn. — The  Changes  in  the 
Cells  op  an  Injured  Part.  —  The  Cells  which  mi- 
grate FROM  the  Blood-vessels  act  as  Phagocytes. — 
The  Macrophages.  —  The  Microphages.  —  Chemo- 
TROPiSM.  —  The  Healing  of  Inflammation.  —  The  Re- 
moval OP  the  Cause.  —  Cell  Repair  and  New 
Formation.  —  New  Formation  of  Blood-vessels.  — 
Acute  and  Chronic  Inflammation.  —  The  appar- 
ently Purposeful  Character  op  the  Changes  m 
Inflammation. 

Injitry  and  repair  have  already  been  briefly 
considered  in  their  relation  to  the  normal  body 
and  to  old  age;  there  are,  however,  certain 
phenomena  included  under  the  term  inflamma- 
tion which  follow  the  more  extensive  injuries  and 
demand  a  closer  consideration  than  was  given 
in  Chapter  11.  These  phenomena  differ  in 
degree  and  character;  they  are  affected  by  the 
nature  of  the  injurious  agent  and  the  intensity 
of  its  action,  by  the  character  of  the  tissue  which 
is  affected  and  by  variations  in  individual  resist- 
ance to  injury.  A  blow  which  would  have  no 
effect  upon  the  general  surface  of  the  body  may 
produce  serious  results  if  it  fall  upon  the  eye, 
79 


80         DISEASE  AND  ITS  CAUSES 

and  less  serious  results  for  a  robust  than  for 
a  weak  individual. 

Most  of  the  changes  which  take  place  after  an 
injury  and  their  sequence  can  be  followed  under 
the  microscope.  If  the  thin  membrane  between 
the  toes  of  a  living  frog  be  placed  under  the 
microscope  the  blood  vessels  and  the  circulating 
blood  can  be  distinctly  seen  in  the  thin  tissue 
between  the  transparent  surfaces.  The  arteries, 
the  capillaries  and  veins  can  be  distinguished, 
the  arteries  by  the  changing  rapidity  of  the 
blood  stream  within  them,  there  being  a  quicken- 
ing of  the  flow  corresponding  with  each  contrac- 
tion of  the  heart  ;  the  veins  appear  as  large 
vessels  in  which  the  blood  flows  regularly  (Fig. 
11).  Between  the  veins  and  arteries  is  a  large 
number  of  capillaries  with  thin  transparent  walls 
and  a  diameter  no  greater  than  that  of  the  single 
blood  corpuscles;  they  receive  the  blood  from  the 
arteries  and  the  flow  in  them  is  continuous. 
The  white  and  red  blood  corpuscles  can  be  dis- 
tinguished, the  red  appearing  as  oval  discs  and 
the  white  as  colorless  spheres.  In  the  arteries  and 
veins  the  red  corpuscles  remain  in  the  centre 
of  the  vessels  appearing  as  a  rapidly  moving 
red  core,  and  between  this  core  and  the  wall  of 
the  vessels  is  a  layer  of  clear  fluid  in  which  the 
white  corpuscles  move  more  slowly,  often  turning 
over  and  over  as  a  ball  rolls  along  the  table. 

If,  now,  the  web  be  injured  by  pricking  it  or 


DISEASE    AND   ITS  CAUSES         81 

placing  some  irritating  substance  upon  it,  a 
change  takes  place  in  the  circulation.  The 
arteries  and  the  veins  become  dilated  and  the 
flow  of  blood  more  rapid,  so  rapid,  indeed,  that 
it  is  difficult  to  distinguish  the  single  corpuscles. 
In  a  short  while  the  rapidity  of  flow  in  the  dilated 
vessels  diminishes,  becoming  slower  than  the 
normal,  and  the  separation  between  the  red  and 
white  corpuscles  is  not  so  evident.  In  the  slowly 
moving  stream  the  white  corpuscles  move  much 
more  slowly  than  do  the  red,  and  hence  accumu- 
late in  the  vessels  lining  the  inner  surface  and 
later  become  attached  to  this  and  cease  to  move 
forward.  The  attached  corpuscles  then  begin 
to  move  as  does  an  amoeba,  sending  out  pro- 
jections, some  one  of  which  penetrates  the  wall, 
and  following  this  the  corpuscles  creep  through. 
Red  corpuscles  also  pass  out  of  the  vessels,  this 
taking  place  in  the  capillaries;  the  white  cor- 
puscles, on  the  other  hand,  pass  through  the 
small  veins.  Not  only  do  the  white  corpuscles 
pass  through  the  vessels,  but  the  blood  fluid 
also  passes  out.  The  corpuscles  which  have 
passed  into  the  tissue  around  the  vessels  are 
carried  away  by  the  outstreaming  fluid,  and  the 
web  becomes  swollen  from  the  increased  amount 
of  fluid  which  it  contains.  The  injured  area  of 
the  web  is  more  sensitive  than  a  corresponding 
uninjured  area  and  the  foot  is  more  quickly 
moved  if  it  be  touched.    If  the  injury  has  been 


82         DISEASE  AND  ITS  CAUSES 

very  slight,  observation  of  the  area  on  the  fol- 
lowing day  will  show  no  change  beyond  a  slight 
dilatation  of  the  vessels  and  a  great  accumulation 
of  cells  in  the  tissue. 

Everyone  has  experienced  the  effect  of  such 
changes  as  have  been  described  in  this  simple 
experiment.  An  inflamed  part  on  the  surface 
of  the  body  is  redder  than  the  normal,  swollen, 
hot  and  painful.  The  usual  red  tinge  of  the  skin 
is  due  to  the  red  blood  contained  in  the  vessels, 
and  the  color  is  intensified  when,  owing  to  the 
dilatation,  the  vessels  contain  more  blood.  The 
inflamed  area  feels  hot,  and  if  the  temperature  be 
taken  it  may  be  two  or  three  degrees  warmer 
than  a  corresponding  area.  The  increased  heat 
is  due  to  the  richer  circulation.  Heat,  is  pro- 
duced in  the  interior  of  the  body  chiefly  in 
the  muscles  and  •  great  glands,  and  the  in- 
creased afflux  of  blood  brings  more  heat  to 
the  surface.  A  certain  degree  of  swelling  of 
the  tissue  is  due  to  the  dilatation  of  the  vessels ; 
but  this  is  a  negligible  factor  as  compared  with 
the  effect  of  the  presence  of  the  fluid  and  cells 
of  the  exudate.^  The  fluid  distends  the  tissue 
spaces,  and  it  may  pass  from  the  tissue  and  ac- 
cumulate on  surfaces  or  in  the  large  cavities 
within  the    body.     The   greatly  increased    dis- 

*  The  term  exudation  is  used  to  designate  the  passing 
of  cells  and  fluid  from  the  vesseb  in  inflammation;  the  mate- 
rial is  the  exudate. 


DISEASE   AND   ITS   CAUSES  83 

charge  from  the  nose  in  a  "cold  in  the  head"  is 
due  to  the  exudation  formed  in  the  acutely  in- 
flamed tissue,  and  which  readily  passes  through 
the  thin  epithelial  covering.  Various  degrees  of 
inflammation  of  the  skin  may  be  produced  by 
the  action  of  the  sun,  the  injury  being  due  not 
to  the  heat  but  to  the  actinic  rays.  In  a 
mild  degree  of  exposure  only  redness  and  a 
strong  sense  of  heat  are  produced,  but  in  pro- 
longed exposure  an  exudate  is  formed  which 
causes  the  skin  to  swell  and  blisters  to  form, 
these  being  due  to  the  exudate  which  passes 
through  the  lower  layers  of  the  cells  of  the 
epidermis  and  collects  beneath  the  impervious 
upper  layer,  detaching  this  from  its  connections. 
If  a  small  wad  of  cotton,  soaked  in  strong  am- 
monia, be  placed  on  the  skin  and  covered  with  a 
thimble  and  removed  after  two  minutes,  minute 
blisters  of  exudate  slowly  form  at  the  spot. 

The  pain  in  an  inflamed  part  is  due  to  a  number 
of  factors,  but  chiefly  to  the  increased  pressure 
upon  the  sensory  nerves  caused  by  the  exudate. 
The  pain  varies  so  greatly  in  degree  and  char- 
acter that  parts  which  ordinarily  have  little 
sensation  may  become  exquisitely  painful  when 
inflamed.  The  pain  is  usually  greater  when  the 
affected  part  is  dense  and  unyielding,  as  the 
membranes  around  bones  and  teeth.  The  pain 
is  often  intermittent,  there  being  acute  paroxysms 
synchronous  with  the  pulse,  this  being  due  to 


84         DISEASE  AND  ITS  CAUSES 

momentary  increase  of  pressure  when  more  blood 
is  forced  into  the  part  at  each  contraction  of 
the  heart.  The  pain  may  also  be  due  to  the 
direct  action  of  an  injurious  substance  upon  the 
sensory  nerves,  as  in  the  case  of  the  sting  of  an 
insect  where  the  pain  is  immediate  and  most 
intense  before  the  exudate  has  begun  to  appear. 

When  an  inflamed  area  is  examined,  after 
twenty-four  hours,  by  hardening  the  tissue  in 
some  of  the  fluids  used  for  this  purpose  and  cut- 
ting it  into  very  thin  slices  by  means  of  an  in- 
strument called  a  microtome,  the  microscope 
shows  a  series  of  changes  which  were  not  appar- 
ent on  naked  eye  examination.  The  texture  is 
looser,  due  to  the  exudate  which  has  dilated  all 
the  spaces  in  the  tissue.  Red  and  white  corpuscles 
in  varying  numbers  and  proportions  infiltrate 
the  tissue;  all  the  cells  which  belong  to  the  part, 
even  those  forming  the  walls  of  the  vessels,  are 
swollen,  the  nuclei  contain  more  chromatin,  and 
the  changes  in  the  nuclei  which  indicate  that 
the  cells  are  multiplying  appear.  The  blood 
vessels  are  dilated,  and  the  part  in  every  way 
gives  the  indication  of  a  more  active  life  within 
it.  There  are  also  evidences  of  the  tissue  in- 
jury which  has  called  forth  all  the  changes  which 
we  have  considered.     (Fig.  15.) 

The  microscopic  examination  of  any  normal 
tissue  of  the  body  shows  within  it  a  variable 
number  of  cells  which  have  no  intimate  associ- 


DISEASE  AND   ITS   CAUSES 


85 


ation  with  the  structure  of  the  part  and  do  not 
seem  to  participate  in  its  function.  They  are 
found  in  situations  which  indicate  that  these 
cells  have  power  of  active  independent  motion. 


Fig.  15.  —  A  section  of  an  inflamed  lung  showing  the 
EXUDATE  WITHIN  THE  AIR  SPACES.  Compare  this  with  Fig.  6. 
Fig.  15  is  from  the  human  lung,  in  which  the  air  spaces  are  much 
larger  than  in  the  mouse. 

In  the  inflamed  tissue  a  greatly  increased  num- 
ber of  these  cells  is  found,  but  they  do  not  ap- 
pear until  the  height  of  the  process  has  passed, 
usually  not  before  thirty-six  or  forty-eight  hours 
after  the  injury  has  been  received.    The  num- 


86 


DISEASE  AND  ITS  CAUSES 


bers  present  depend  much  upon  the  character  of 
the  agent  which  has  produced  the  injury,  and 
they  may  be  more  numerous  than  the  ordinary 
leucocytes  which  migrate  from  the  blood  vessels. 
All  these  changes  which  an  injured  part  under- 
goes are  found  when  closely  analyzed  to  be 
purposeful;  that  is,  they  are  in  accord  with  the 


Fig.  16.  —  Phagocytosis,  a,  b,  c  are  the  microphages 
or  the  bacterial  phagocytes,  (a)  Contains  a  number  of  round 
bacteria,  and  (b)  similar  bacteria  arranged  in  chains,  and  (c) 
a  number  of  rod-shaped  bacteria,  (d)  Is  a  cell  phagocyte 
or  macrophage  which  contains  five  red  blood  corpuscles. 

conditions  under  which  the  living  matter  acts, 
and  they  seem  to  facilitate  the  operation  of 
these  conditions.  It  has  been  said  that  the  life 
of  the  organism  depends  upon  the  coordinated 
activity  of  the  living  units  or  cells  of  which  it  is 
composed.  The  cells  receive  from  the  blood 
material  for  the  purpose  of  function,  for  cell 
repair  and  renewal,  and  the  products  of  waste 


DISEASE  AND   ITS   CAUSES  87 

must  be  removed.  In  the  injury  which  has 
been  produced  in  the  tissue  all  the  cells  have 
suffered,  some  possibly  displaced  from  their 
connections,  others  may  have  been  completely 
destroyed,  others  have  sustained  varying  degrees 
of  injury.  If  the  injury  be  of  an  infectious  char- 
acter, that  is,  produced  by  bacteria,  these  may 
be  present  in  the  part  and  continue  to  exert 
injury  by  the  poisonous  substances  which  they 
produce,  or  if  the  injury  has  been  produced  by 
the  action  of  some  other  sort  of  poison,  this  may 
be  present  in  concentrated  form,  or  the  injury 
may  have  been  the  result  of  the  presence  of  a 
foreign  body  in  the  part.  Under  these  conditions, 
since  the  usual  activities  of  the  cells  in  the  injured 
part  will  not  suffice  to  restore  the  integrity  of 
the  tissue,  repair  and  cell  formation  must  be 
more  active  than  usual,  any  injurious  substances 
must  be  removed  or  such  changes  must  take 
place  in  the  tissue  that  the  cell  life  adapts  itself 
to  new  conditions. 

All  life  in  the  tissues  depends  upon  the  circu- 
lation of  the  blood.  There  is  definite  relation 
between  the  activity  of  cells  and  the  blood  supply; 
a  part,  for  instance,  which  is  in  active  function 
receives  a  greater  supply  of  blood  by  means  of 
dilatation  of  the  arteries  which  supply  it.  If  the 
body  be  exactly  balanced  longitudinally  on  a 
platform,  reading  or  any  exercise  of  the  brain 
causes  the  head  end  to  sink  owing  to  the  relatively 


88  DISEASE  AND   ITS   CAUSES 

greater  amount  of  blood  which  the  brain  re- 
ceives when  in  active  function.  The  regulation 
of  the  blood  supply  is  effected  by  means  of 
nerves  which  act  upon  the  muscular  walls  of 
the  arteries  causing,  by  the  contraction  or  the 
relaxation  of  the  muscle,  diminution  or  dilata- 
tion of  the  calibre  of  the  vessel.  After  injury 
the  dilatation  of  the  vessels  with  the  greater 
aflBlux  of  blood  to  the  part  is  the  effect  of  the 
greatly  increased  cell  activity,  and  is  a  neces- 
sity for  this.  In  many  forms  of  disease  it  has 
been  found  that  by  increasing  the  blood  flow 
to  a  part  and  producing  an  active  circulation 
in  it,  that  recovery  more  readily  takes  place  and 
many  of  the  procedures  which  have  been  found 
useful  in  inflammation,  such  as  hot  applications, 
act  by  increasing  the  blood  flow.  So  intimate 
is  the  association  between  cell  activity,  as  shown 
in  repair  and  new  formation  of  cells,  and  the 
blood  flow,  that  new  blood  vessels  frequently 
develop  by  means  of  which  the  capacity  for 
nutrition  is  still  more  increased.  The  cornea 
or  transparent  part  of  the  eye  contains  no  blood 
vessels,  the  cells  which  it  contains  being  nour- 
ished by  the  tissue  fluid  which  comes  from  the 
outside  and  circulates  in  small  communicating 
spaces.  If  the  centre  of  the  cornea  be  injured, 
the  cells  of  the  blood  vessels  in  the  tissue 
around  the  cornea  multiply  and  form  new  ves- 
sels which  grow  into  the  cornea  and  appear  as  a 


DISEASE  AND   ITS   CAUSES  89 

pink  fringe  around  the  periphery;  when  repair 
has  taken  place  the  newly  formed  vessels  dis- 
appear. 

The  exudate  from  the  blood  vessels  in  various 
ways  assists  in  repair.  An  injurious  substance 
in  the  tissue  may  be  so  diluted  by  the  fluid  that 
its  action  is  minimized.  A  small  crystal  of  salt 
is  irritating  to  the  eye,  but  a  much  greater  amount 
of  the  same  substance  in  dilute  solution  causes 
no  irritation.  The  poisonous  substances  produced 
by  bacteria  are  diluted  and  washed  away  from 
the  part  by  the  exudate.  Not  only  is  there  a 
greater  amount  of  tissue  fluid  in  the  inflamed 
part,  but  the  circulation  of  this  is  also  in- 
creased, as  is  shown  by  comparing  the  outflow 
in  the  lymphatic  vessels  with  the  normal.  The 
fluid  exudate  which  has  come  from  the  blood 
and  differs  but  slightly  from  the  blood  fluid 
exerts  not  only  the  purely  physical  action  of 
removing  and  diluting  injurious  substances,  but 
in  many  cases  has  a  remarkable  power,  exer- 
cised particularly  on  bacterial  poisons,  of  neu- 
tralizing poisons  or  so  changing  their  character 
that  they  cease  to  be  injurious. 

We  have  learned,  chiefly  from  the  work  of 
Metschnikoff ,  that  those  white  corpuscles  or  leu- 
cocytes which  migrate  from  the  vessels  in  the 
greatest  numbers  have  marked  phagocytic  prop- 
erties, that  is,  they  can  devour  other  living 
things  and  thus  destroy  them  just  as   do  the 


90         DISEASE  AND   ITS  CAUSES 

amoebae.  In  inflammations  produced  by  bacteria 
there  is  a  very  active  migration  of  these  cells 
from  the  vessels;  they  accumulate  in  the  tissue 
and  devour  the  bacteria.  They  may  be  present 
in  such  masses  as  to  form  a  dense  wall  around 
the  bacteria,  thus  acting  as  a  physical  bar  to 
their  further  extension.  The  other  form  of 
amoeboid  cell,  which  Metschnikoff  calls  the 
macrophage,  has  more  feeble  phagocytic  action 
towards  bacteria,  and  these  are  rarely  found 
enclosed  within  them.  It  is  chiefly  by  means 
of  their  activity  that  other  sorts  of  substances 
are  removed.  They  often  contain  dead  cells  or 
cell  fragments,  and  when  haemorrhage  takes 
place  in  a  tissue  they  enclose  and  remove  the 
granules  of  blood  pigment  which  result.  They 
often  join  together,  forming  connected  masses, 
and  surround  such  a  foreign  body  as  a  hair,  or  a 
thread  which  the  surgeon  places  in  a  wound  to 
close  it.  They  may  destroy  Uving  cells,  and  do 
this  seemingly  when  certain  cells  are  in  too  great 
numbers  and  superfluous  in  a  part,  tlieir  action 
tending  to  restore  the  cell  equilibrium.  The 
foreign  cells  do  even  more  than  this :  they  them- 
selves may  be  devoured  by  the  growing  cells  of 
the  tissue,  seemingly  being  actuated  by  the  same 
supreme  idea  of  sacrifice  which  led  Buddha  to 
give  himself  to  the  tigress. 

The  explanation  of  most  of  the  changes  which 
take  place  in  inflammation  is  obvious.     It  is  a 


DISEASE  AND   ITS   CAUSES  91 

definite  property  of  all  living  things  that  repair 
takes  place  after  injury,  and  certain  of  the  changes 
are  only  an  accentuation  of  those  which  take 
place  in  the  usual  life;  but  others,  such  as  the 
formation  of  the  exudate,  are  unusual;  not  only 
is  the  outpouring  of  fluid  greatly  increased,  but 
its  character  is  changed.  In  the  normal  tran- 
sudation ^  the  substances  on  which  the  coagu- 
lation of  the  blood  depends  pass  through  the 
vessel  wall  to  a  very  slight  extent,  but  the  exu- 
date may  contain  the  coagulable  material  in  such 
amounts  that  it  easily  clots.  The  interchange 
between  the  fluid  outside  the  vessels  and  the 
blood  fluid  takes  place  by  means  of  filtration  and 
osmosis.  There  is  a  greater  pressure  in  the 
vessels  than  in  the  fluid  outside  of  them,  and  the 
fluid  filters  through  the  wall  as  fluid  filters  through 
a  thin  membrane  outside  of  the  body.  Osmosis 
takes  place  when  two  fluids  of  different  osmotic 
pressure  are  separated  by  animal  membrane. 
Difference  in  osmotic  pressure  is  due  to  differ- 
ences in  molecular  concentration,  the  greater 
the  number  of  molecules  the  greater  is  the  pres- 
sure, and  the  greater  rapidity  of  flow  is  from  the 
fluid  of  less  pressure  to  the  fluid  of  greater  pres- 
sure. The  molecular  concentration  of  tissue  and 
blood  fluid  is  constantly  being  equalized  by  the 
process  of  osmosis.     In  the  injured  tissue  the 

^  By   transudation    is   meant   the   constant   interchange 
between  the  blood  and  the  tissue  fluid. 


92         DISEASE  AND   ITS  CAUSES 

conditions  are  more  favorable  for  the  fluid  of 
the  blood  to  pass  from  the  vessels :  by  filtration, 
because  owing  to  the  dilatation  of  the  arteries  there 
is  increased  amount  of  blood  and  greater  pressure 
within  the  vessels,  and  the  filtering  membrane 
is  also  thinner  because  the  same  amount  of 
membrane  (here  the  wall  of  the  vessel)  must 
cover  the  larger  surface  produced  by  the  dilata- 
tion. It  is,  moreover,  very  generally  believed 
that  there  are  minute  openings  in  the  walls  of  the 
capillaries,  and  these  would  become  larger  in 
the  dilated  vessel  just  as  openings  in  a  sheet  of 
rubber  become  larger  when  this  is  stretched. 
Osmosis  towards  the  tissue  is  favored  because, 
owing  to  destructive  processes  the  molecular 
pressure  in  the  injured  area  is  increased;  an  in- 
jured tissue  has  been  shown  to  take  up  fluid 
more  readily  outside  of  the  body  than  a  corre- 
sponding uninjured  tissue.  The  slowing  of  the 
blood  stream,  in  spite  of  the  dilatation  of  the 
vessels,  is  due  to  the  greater  friction  of  the  sus- 
pended corpuscles  on  the  walls  of  the  vessels. 
This  is  due  to  the  loss  from  the  blood  of  the 
outstreaming  fluid  and  the  relative  increase  in 
the  number  of  corpuscles,  added  to  by  the  un- 
evenness  of  surface  which  the  attached  corpuscles 
produce. 

The  wonderful  migration  of  the  leucocytes, 
which  seems  to  show  a  conscious  protective  action 
on  their  part,  takes  place  under  the  action  of 


DISEASE  AND   ITS   CAUSES  93 

conditions  which  influence  the  movement  of  cells. 
When  an  actively  moving  amoeba  is  observed  it  is 
seen  that  the  motion  is  not  the  result  of  chance, 
for  it  is  influenced  by  conditions  external  to  the 
organism;  certain  substances  are  found  to  at- 
tract the  amoebae  towards  them  and  other  sub- 
stances to  repel  them.  These  influences  or  forces 
affecting  the  movements  of  organisms  are  known 
as  tropisms,  and  play  a  large  part  in  nature; 
the  attraction  of  various  organisms  towards  a 
source  of  light  is  known  as  heliotropism,  and 
there  are  many  other  instances  of  such  attrac- 
tion. The  leucocytes  as  free  moving  cells  also 
come  under  the  influence  of  such  tropisms. 
When  a  small  capillary  tube  having  one  end 
sealed  is  partially  filled  with  the  bacteria  which 
produce  abscess  and  placed  beneath  the  skin 
it  quickly  becomes  filled  with  leucocytes,  these 
being  attracted  by  the  bacteria  it  contains. 
Dead  cells  exert  a  similar  attraction  for  the 
large  phagocytes.  Such  attraction  is  called 
chemotropism  and  is  supposed  to  be  due  in  the 
cases  mentioned,  to  the  action  of  chemical  sub- 
stances such  as  are  given  off  by  the  bacteria  or 
the  dead  cells.  The  direction  of  motion  is  due  to 
stimulation  of  that  part  of  the  body  of  the  leuco- 
cyte which  is  towards  the  source  of  the  stimulus. 
The  presence  in  the  injured  part  of  bacteria  or 
of  injured  and  dead  cells  exerts  an  attraction 
for   the   leucocytes   within   the   vessels   causing 


94         DISEASE  AND  ITS  CAUSES 

their  migration.  When  the  centre  of  the  cornea 
is  injured,  this  tissue  having  no  vessels,  all  the 
vascular  phenomena  take  place  in  the  white 
part  of  the  eye  immediately  around  the  cornea, 
this  becoming  red  and  congested.  The  migra- 
tion of  leucocytes  from  the  vessels  takes  place 
chiefly  on  the  side  towards  the  cornea,  and  the 
migrated  cells  make  their  way  along  the  devious 
tracts  of  the  communicating  lymph  spaces  to  the 
area  of  injury.  The  objection  may  be  raised  that 
it  is  difficult  to  think  of  a  chemical  substance  pro- 
duced in  an  injured  area  no  larger  than  a  milli- 
meter, diffusing  through  the  cornea  and  reaching 
the  vessels  outside  this  in  such  quantity  and 
concentration  as  to  affect  their  contents,  nor 
has  there  been  any  evidence  presented  that 
definite  chemical  substances  are  produced  in 
injured  tissues;  but  there  is  no  difficulty  in  view 
of  the  possibilities.  It  is  not  necessary  to  assume 
that  an  actual  substance  so  diffuses  itself,  but 
the  influence  exerted  may  be  thought  of  as  a 
force,  possibly  some  form  of  molecular  motion, 
which  is  set  in  action  at  the  area  of  injury  and 
extends  from  this.  No  actual  substance  passes 
along  a  nerve  when  it  conveys  an  impulse. 

We  have  left  the  injured  area  with  an  increased 
amount  of  fluid  and  cells  within  it,  with  the 
blood  vessels  dilated  and  with  both  cells  and 
fluid  streaming  through  their  walls,  and  the  cells 
belonging  to  the  area  actively  repairing  damages 


DISEASE  AND   ITS   CAUSES  95 

and  multiplying.  The  process  will  continue  as 
long  as  the  cause  which  produces  the  injury  con- 
tinues to  act,  and  will  gradually  cease  with  the 
discontinuance  of  this  action,  and  this  may  be 
brought  about  in  various  ways.  A  foreign  body 
may  be  mechanically  removed,  as  when  a  thorn 
is  plucked  out;  or  bacteria  may  be  destroyed  by 
the  leucocytes;  or  a  poison,  such  as  the  sting  of 
an  insect,  may  be  diluted  by  the  exudate  until 
it  be  no  longer  injurious,  or  it  may  be  neutralized. 
Even  without  the  removal  of  the  cause  the  power 
of  adaptation  will  enable  the  life  of  the  affected 
part  to  go  on,  less  perfectly  perhaps,  in  the  new 
environment.  The  excess  of  fluid  is  removed 
by  the  outflow  exceeding  the  inflow,  or  it  may 
pass  to  some  one  of  the  surfaces  of  the  body, 
or  in  other  cases  an  incision  favors  its  escape. 
The  excess  of  cells  is  in  part  removed  with  the 
fluid,  in  part  they  disappear  by  undergoing 
solution  and  in  part  they  are  devoured  by  other 
cells.  With  the  diminishing  cell  activity  the 
blood  vessels  resume  their  usual  calibre,  and  when 
the  newly  formed  vessels  become  redundant  they 
disappear  by  undergoing  atrophy  in  the  same 
way  as  other  tissues  which  have  become  useless. 

When  these  changes  take  place  rapidly  the 
inflammation  is  said  to  be  acute,  and  chronic 
when  they  take  place  slowly.  Chronic  inflamma- 
tion is  more  complex  than  is  the  acute,  and  there 
is  more  variation  in  the  single  conditions.     The 


96         DISEASE  AND   ITS  CAUSES 

chronicity  may  be  due  to  a  number  of  condi- 
tions, as  the  persistence  of  a  cause,  or  to  incom- 
pleteness of  repair  which  renders  the  part  once 
affected  more  vulnerable,  to  such  a  degree  even 
that  the  ordinary  conditions  to  which  it  is  sub- 
jected become  injurious,  A  chronic  inflammation 
may  be  little  more  than  an  almost  continuous 
series  of  acute  inflammations,  with  repair  continu- 
ously less  perfect.  Chronic  imflammations  are  a 
prerogative  of  the  old  as  compared  with  the 
young,  of  the  weak  rather  than  the  strong. 


CHAPTER  V 

Infectious  Diseases.  —  The  Historical  Importance  op 
Epidemics  of  Disease.  —  The  Losses  in  Battle  con- 
trasted WITH  THE  Losses  in  Armies  produced  by 
Infectious  Diseases.  —  The  Development  of  Knowl- 
edge OF  Epidemics. — The  Views  of  Hippocrates 
and  Aristotle.  —  Sporadic  and  Epidemic  Diseases.  — 
The  Theory  of  the  Epidemic  Constitution.  —  Theory 
that  the  Contagious  Material  is  Living.  —  The 
Discovery  of  Bacteria  by  Ixewenhoeck  in  1675.  — 
The  Relation  of  Contagion  to  the  Theory  of 
Spontaneous  Generation.  —  Needham  and  Spallan- 
ZANi.  —  The  Discovery  of  the  Compound  Microscope 
IN  1605. — The  Proof  that  a  living  Organism  is  the 
Cause  of  a  Disease.  —  Anthrax.  —  The  Discovery  of 
the  Anthrax  Bacillus  in  1851. — The  Cultivation 
of  the  Bacillus  by  Koch.  —  The  Mode  of  Infec- 
tion. —  The  Work  of  Pasteur  on  Anthrax.  —  The 
Importance  of  the  Disease. 

These  are  diseases  which  are  caused  by  living 
things  which  enter  the  tissues  of  the  body  and, 
living  at  the  expense  of  the  body,  produce  injury. 
Such  diseases  play  an  important  part  in  the  life 
of  man;  the  majority  of  deaths  are  caused  di- 
rectly or  indirectly  by  infection.  No  other  diseases 
have  been  so  much  studied,  and  in  no  other 
department  of  science  has  knowledge  been  cap- 
able of  such  direct  application  in  promoting  the 
health,  the  efficiency  and  the  happiness  of  man. 
This  knowledge  has  added  years  to  the  average 
length  of  life,  it  has  rendered  possible  such  great 
engineering  works  as  the  Panama  Canal,  and 
has  contributed  to  the  food  supply  by  making 
97 


98         DISEASE  AND   ITS  CAUSES 

habitation  possible  over  large  and  productive 
regions  of  the  earth,  formerly  uninhabitable 
owing  to  the  prevalence  of  disease.  It  is  not  too 
much  to  say  that  our  modern  civilization  is 
dependent  upon  this  knowledge.  The  massing 
of  the  people  in  large  cities,  the  factory  life,  the 
much  greater  social  life,  which  are  all  prominent 
features  of  modem  civilization,  would  be  diflBcult 
or  impossible  without  control  of  the  infectious 
diseases.  The  rapidity  of  communication  and 
the  increased  general  movement  of  people,  which 
have  developed  in  equal  ratio  with  the  massing, 
would  serve  to  extend  widely  every  local  out- 
break of  infection.  The  principles  underlying 
fermentation  and  putrefaction  which  have  been 
applied  with  great  economic  advantage  to  the 
preservation  of  food  were  many  of  them  developed 
in  the  course  of  the  study  of  the  infectious  dis- 
eases. Whether  the  development  of  the  present 
civilization  is  for  the  ultimate  advantage  of  man 
may  perhaps  be  disputed,  but  medicine  has 
made  it  possible. 

The  infectious  diseases  appearing  in  the  form 
of  great  epidemics  have  been  important  factors 
in  determining  historical  events,  for  they  have 
led  to  the  defeat  of  armies,  the  fall  of  cities  and 
of  nations.  War  is  properly  regarded  as  one  of 
the  greatest  evils  that  can  afflict  a  nation,  since 
it  destroys  men  in  the  bloom  of  youth,  at  the 
age  of  greatest  service,  and  brings  sorrow  and  care 


DISEASE   AND   ITS  CAUSES  99 

and  poverty  to  many.  But  the  most  potent 
factor  in  the  losses  of  war  is  not  the  deaths  in 
battle  but  the  deaths  from  disease.  If  we  desig- 
nate the  lives  lost  in  battle,  the  killed  and  the 
wounded  who  die,  as  1,  the  loss  of  the  German 
army  from  disease  in  1870-71  was  1.5,  that  of 
the  Russians  in  1877-78  was  2.7,  that  of  the 
French  in  Mexico  was  2.8,  that  of  the  French 
in  the  Crimea  3.7,  that  of  the  English  in  Egypt 
4.2.  The  total  loss  of  the  German  army  in 
1870-71  from  wounds  and  disease  was  43,182 
oflScers  and  men,  and  this  seems  a  small  number 
compared  with  the  129,128  deaths  from  small- 
pox in  the  same  period  in  Prussia  alone.  In  the 
Spanish  American  war  there  were  20,178  cases 
of  typhoid  fever  with  1,580  deaths.  In  the  South 
African  war  there  were  in  the  British  troops 
31,118  cases  of  typhoid  with  5,877  deaths,  and 
5,149  deaths  from  other  diseases  while  the  loss 
in  battle  was  7,582.  The  Athenian  plague  which 
prevailed  during  the  Peloponnesian  war,  431- 
405  B.  c,  not  only  caused  the  death  of  Pericles, 
but  according  to  Thucydides  a  loss  of  4,800 
Athenian  soldiers,  and  brought  about  the  down- 
fall of  the  Athenian  hegemony  in  Greece.  In 
the  Crimean  war  between  1853-56,  16,000 
English,  80,000  French  and  800,000  Russians 
died  of  typhus  fever.  The  plague  contributed 
as  much  as  did  the  arms  of  the  Turks  to  the 
downfall    of    Constantinople    and    the    Eastern 


100       DISEASE  AND  ITS  CAUSES 

Empire  in  1453.  It  was  the  plague  which  in 
1348  overthrew  Siena  from  her  proud  position 
as  one  of  the  first  of  the  Italian  cities  and  the 
rival  of  Florence,  and  broke  the  city  forever, 
leaving  it  as  a  phantom  of  its  former  glory  and 
prosperity.  The  work  on  the  great  cathedral 
which  had  progressed  for  ten  years  was  suspended, 
and  when  it  was  resumed  it  was  upon  a  scale 
adjusted  to  the  diminished  wealth  of  the  city, 
and  the  plan  restricted  to  the  present  dimensions. 
As  a  httle  relief  to  the  darkness  the  same  plague 
saw  the  birth  of  the  novel  in  the  tales  of  Boccac- 
cio, which  were  related  to  a  delighted  audience 
of  the  women  who  had  fled  from  the  plague  in 
Florence  to  a  rural  retreat. 

The  knowledge  which  has  come  from  the  study 
of  infectious  disease  has  served  also  to  broaden 
our  conception  of  disease  and  has  created  pre- 
ventive medicine;  it  has  linked  more  closely  to 
medicine  such  sciences  as  zoology  and  botany; 
it  has  given  birth  to  the  sciences  of  bacteriology 
and  protozoology  and  in  a  way  has  brought  all 
sciences  more  closely  together.  Above  all  it 
has  made  medicine  scientific,  and  never  has 
knowledge  obtained  been  more  quickening  and 
stimulating  to  its  pursuit. 

Although  the  dimensions  of  this  book  forbid 
much  reference  to  the  historical  development 
of  a  subject,  some  mention  must  still  be  made 
of  the  development  of  knowledge  of  the  infec- 


DISEASE  AND   ITS   CAUSES        101 

tious  diseases.  It  was  early  recognized  that 
there  were  diseases  which  differed  in  character 
from  those  generally  prevalent;  large  numbers 
of  people  were  affected  in  the  same  way;  the 
disease  beginning  with  a  few  cases  gradually 
increased  in  intensity  until  an  acme  was  reached 
which  prevailed  for  a  time  and  the  disease  gradu- 
ally disappeared.  Such  diseases  were  attributed 
to  changes  in  the  air,  to  the  influence  of  planets 
or  to  the  action  of  offended  gods.  The  priests 
and  charlatans  who  sought  to  excuse  their  in- 
ability to  treat  epidemics  successfully  were  quick 
to  affirm  supernatural  causes.  Hippocrates 
(400  B.  c),  with  whom  medicine  may  be  said  to 
begin,  thought  such  diseases,  even  then  called 
epidemics,  were  caused  by  the  air;  he  says, 
"When  many  individuals  are  attacked  by  a 
disease  at  the  same  time,  the  cause  must  be 
sought  in  some  agent  which  is  common  to  all, 
something  which  everyone  uses,  and  that  is  the 
air  which  must  contain  at  this  time  something 
injurious."  Aristotle  recognized  that  disease 
was  often  conveyed  by  contact,  and  Varro  (116- 
27  B.  c.)  advanced  the  idea  that  disease  might  be 
caused  by  minute  organisms.  He  says,  "  Certain 
minute  organisms  develop  which  the  eye  cannot 
see,  and  which  being  disseminated  in  the  air 
enter  into  the  body  by  means  of  the  mouth  and 
nostrils  and  give  rise  to  serious  ailments."  In 
spite  of  this  hypothesis,  which  has  proved  to  be 


102        DISEASE  AND   ITS   CAUSES 

correct,  the  belief  became  general  that  epidemics 
were  due  to  putrefaction  of  the  air  brought  about 
by  decaying  animal  bodies,  (this  explaining  the 
frequent  association  of  epidemics  and  wars,)  by 
emanations  from  swamps,  by  periods  of  unusual 
heat,  etc. 

With  the  continued  study  of  epidemics  the 
importance  of  contagion  was  recognized;  it  was 
found  that  epidemics  differed  in  character  and 
in  the  modes  of  extension.  Some  seemed  to 
extend  by  contact  with  the  sick,  and  in  others 
this  seemed  to  play  no  part;  it  was  further  found 
impossible  in  many  cases  to  show  evidence  of 
air  contamination,  and  contamination  of  the 
air  by  putrefactive  material  did  not  always 
produce  disease.  Most  important  was  the  recog- 
nition that  single  cases  of  diseases  which  often 
occurred  in  epidemic  form  might  be  present  and 
no  further  extension  follow;  this  led  to  the  as- 
sumption in  epidemics  of  the  existence  of  some 
condition  in  addition  to  the  cause,  and  which 
made  the  cause  operative.  In  this  way  arose 
the  theory  of  the  epidemic  constitution,  a  sup- 
posed peculiar  condition  of  the  body  due  to 
changes  in  the  character  of  the  air,  or  to  the 
climate,  or  to  changes  in  the  interior  of  the  earth 
as  shown  by  earthquakes,  or  to  the  movements 
of  planets;  in  consequence  of  this  pecuHar 
constitution  there  was  a  greater  susceptibility 
to  disease,  but  the  direct  cause  might  arise  in 


DISEASE  AND  ITS  CAUSES        103 

the  interior  of  the  body  or  enter  the  body  from 
without.  The  character  of  the  disease  which 
appeared  in  epidemic  form,  the  "Genius  epidem- 
icus,"  was  determined  not  by  differences  in  the 
intrinsic  cause,  but  by  the  type  of  constitution 
which  prevailed  at  that  time.  The  first  epidemic 
of  cholera  which  visited  Europe  in  1830-37  was 
for  the  most  part  referred  to  the  existence  of  a 
peculiar  epidemic  constitution  for  which  various 
causes  were  assigned.  It  was  only  when  the 
second  epidemic  of  this  disease  appeared  in  1840 
that  the  existence  of  some  special  virus  or  poison 
which  entered  the  body  was  assumed. 

Meanwhile,  by  the  study  of  the  material  of 
disease  knowledge  was  being  slowly  acquired 
which  had  much  bearing  on  the  causes.  The 
first  observations  which  tended  to  show  that  the 
causes  were  living  were  made  by  a  learned  Jesuit, 
Athanasius,  in  1659.  He  found  in  milk,  cheese, 
vinegar,  decayed  vegetables,  and  in  the  blood 
and  secretions  of  cases  of  plague  bodies,  which  he 
described  as  tiny  worms  and  which  he  thought 
were  due  to  putrefaction.  He  studied  these 
objects  with  the  simple  lenses  in  use  at  that  time, 
and  there  is  little  doubt  that  he  did  see  certain 
of  the  larger  organisms  which  are  present  in 
vinegar,  cheese  and  decaying  vegetables,  and  it 
is  not  impossible  that  he  may  have  seen  the 
animal  and  vegetable  cells. 

The  first  description  of  bacteria  with  illustra- 


104       DISEASE  AND  ITS  CAUSES 

tions  showing  their  forms  was  given  by  Loe- 
wenhoeck,  a  linen  dealer  in  Amsterdam  in  1675. 
The  fineness  of  the  linen  being  determined  by 
the  number  of  threads  in  a  given  area,  it  is 
necessary  to  examine  it  with  a  magnifying  lens, 
and  he  succeeded  in  perfecting  a  simple  lens 
with  which  objects  smaller  than  had  been  seen 
up  to  that  time  became  visible.  It  must 
be  added  that  he  was  probably  endowed  with 
very  unusual  acuteness  of  vision.  He  found  in 
a  drop  of  water,  in  the  fluid  in  the  intestines  of 
frogs  and  birds,  and  in  his  evacuations,  objects 
of  great  minuteness  which  differed  from  each 
other  in  form  and  size  and  in  the  peculiar  motion 
which  some  of  them  possessed.  In  the  year  1683 
he  presented  to  the  Royal  Society  of  London  a 
paper  describing  a  certain  minute  organism 
which  he  found  in  the  tartar  of  his  teeth.  After 
these  observations  of  Loewenhoeck  became  known 
to  the  world  they  quickly  found  application  in 
disease,  although  the  author  had  expressed  him- 
self very  cautiously  in  this  regard.  The  strongest 
exponent  of  the  view  of  a  living  contagion  was 
Plenciz,  1762,  a  physician  of  Vienna,  basing 
his  belief  not  only  on  the  demonstration  of  minute 
organisms  by  Loewenhoeck  which  he  was  able 
to  verify,  but  on  certain  shrewdly  conceived 
theoretical  considerations.  He  was  the  first  to 
recognize  the  specificity  of  the  epidemic  diseases, 
and  argued  from  this  that  each  disease  must 


DISEASE  AND   ITS  CAUSES        105 

have  a  specific  cause.  "Just  as  a  certain  plant 
comes  from  the  seed  of  the  same  plant  and  not 
from  any  plant  at  will,  so  each  contagious  disease 
must  be  propagated  from  a  similar  disease  and 
cannot  be  the  result  of  any  other  disease."  Fur- 
ther he  says,  "It  is  necessary  to  assume  that 
during  the  prevalence  of  an  epidemic  the  con- 
tagious material  undergoes  an  enormous  increase, 
and  this  is  compatible  only  with  the  assumption 
that  it  is  a  Uving  substance."  But  as  is  so  often 
the  case,  speculation  ran  far  ahead  of  the  obser- 
vations on  which  it  is  based.  There  was  a  long 
gap  between  the  observations  of  Loewenhoeck 
and  the  theories  of  Plenciz,  justified  as  these 
have  been  by  present  knowledge.  In  the  spirit 
of  speculation  which  was  dominant  in  Europe  and 
particularly  in  Germany  in  the  latter  half  of  the 
eighteenth  and  the  first  half  of  the  nineteenth 
centuries,  hypotheses  did  not  stimulate  research, 
but  led  to  further  speculations.  As  late  as  1820 
Ozanam  expressed  himself  as  follows:  "Many 
authors  have  written  concerning  the  animal 
nature  of  the  contagion  of  disease;  many  have 
assumed  it  to  be  developed  from  animal  sub- 
stance, and  that  it  is  itself  animal  and  possesses 
the  property  of  life.  I  shall  not  waste  time  in 
refuting  these  absurd  hypotheses."  The  theory 
of  a  living  contagion  was  too  simple,  and  not 
sufficiently  related  to  the  problems  of  the  universe 
to  serve  the  medical  philosophers. 


106       DISEASE  AND  ITS  CAUSES 

Knowledge  of  the  minute  organisms  was  slowly 
accumulating.  The  first  questions  to  be  deter- 
mined were  as  to  their  nature  and  origin.  How 
were  they  produced?  Did  they  come  from  bodies 
of  the  same  sort  according  to  the  general  laws 
governing  the  production  of  living  things,  or  did 
they  arise  spontaneously?  a  question  which 
could  not  be  solved  by  speculation  but  by  experi- 
ment. The  first  experiments,  by  Needham,  1745, 
pointed  to  the  spontaneous  origin  of  the  organ- 
isms. He  enclosed  various  substances  in  care- 
fully sealed  watch  crystals  from  which  the  air 
was  excluded,  and  found  that  animalculi  ap- 
peared in  the  substance,  and  argued  from  this 
that  they  developed  spontaneously.  In  1769, 
Spallanzani,  a  skilled  experimental  physiologist, 
in  a  brilliant  series  of  experiments  showed  the 
imperfect  character  of  Needham's  work  and  the 
fallacy  of  his  conclusions.  Spallanzani  placed 
fluids,  which  easily  became  putrid,  in  glass  tubes, 
which  he  then  hermetically  sealed  and  boiled. 
He  found  that  the  fluid  remained  clear  and  un- 
changed; if,  however,  he  broke  the  sealed  point 
of  such  a  tube  and  allowed  the  air  to  enter, 
putrefaction,  or  in  some  cases  fermentation,  of 
the  contents  took  place.  He  concluded  that 
boiling  the  substances  destroyed  the  living  germs 
which  they  contained,  the  sealed  tubes  prevented 
the  air  from  entering,  and  when  putrefaction 
or  fermentation  of  the  contents  took  place  the 


DISEASE  AND   ITS   CAUSES        107 

organisms  to  which  this  was  due,  being  con- 
tained in  the  air,  entered  from  without.  Objec- 
tion was  made  to  the  conclusions  of  Spallanzani 
that  heating  the  air  in  the  closed  tubes  so  changed 
its  character  as  to  prevent  development  of  organ- 
isms in  the  contents.  This  objection  was  finally 
set  aside  by  Pasteur,  who  showed  that  it  was  not 
necessary  to  seal  the  end  of  the  tube  before  boiling, 
but  it  could  be  closed  by  a  plug  of  cotton  wool, 
which  mechanically  removed  the  organisms  from 
the  air  which  entered  the  tube,  or  if  the  tube 
were  bent  in  the  shape  of  a  C/  and  the  end  left 
open,  organisms  from  the  air  could  not  pass  into 
the  tube  against  gravity  when  air  movement 
within  the  tube  was  prevented  by  bending. 
The  possibility  of  spontaneous  generation  can- 
not be  denied,  but  that  it  takes  place  is  against 
all  human  experience. 

It  was  not  possible  to  attain  any  considerable 
knowledge  of  the  Jbacteria  discovered  by  Loe- 
wenhoeck  until  more  perfect  instruments  for 
studying  them  were  devised.  Lenses  for  studying 
objects  were  used  in  remote  antiquity,  but  the 
compound  microscope  in  which  the  image  made 
by  the  lens  is  further  magnified  was  not  dis- 
covered until  1605,  and  when  first  made  was  so 
imperfect  that  the  best  simple  lenses  gave  clearer 
definition.  With  the  betterment  of  the  micro- 
scope, increasing  the  magnifying  power  and  the 
sharpness  of  the  image  of  the  object  seen,  it  became 


108       DISEASE  AND  ITS  CAUSES 

possible  to  classify  the  minute  organisms  accord- 
ing to  size  and  form  and  to  study  the  separate 
species.  The  microscope  has  now  reached  such 
a  degree  of  perfection  that  objects  smaller  than 
one  one  hundred  thousandth  of  an  inch  in  diam- 
eter can  be  clearly  seen  and  photographed. 

Great  impetus  was  given  to  the  biological 
investigation  of  disease  by  the  discoveries  which 
led  to  the  formulation  of  the  cell  theory  in  1840 
and  the  brilliant  work  of  Pasteur  on  fermentation,^ 
but  it  was  not  until  1878  that  it  was  definitely 

1  The  interesting  analogy  between  fermentation  and 
infectious  disease  did  not  escape  attention.  A  clear  fluid 
containing  in  solution  sugar  and  other  constituents  necessary 
for  the  life  of  the  yeast  cells  will  remain  clear  provided  all 
living  things  within  it  have  been  destroyed  and  those  in  the 
air  prevented  from  entering.  If  it  be  inoculated  with  a 
minute  fragment  of  yeast  culture  containing  a  few  yeast 
cells,  for  a  time  no  change  takes  place;  but  gradually  the 
fluid  becomes  cloudy,  bubbles  of  gas  appear  in  it  and  its  taste 
changes.  Finally  it  again  becomes  clear,  a  sediment  forms 
at  the  bottom,  and  on  re-inoculating  it  with  yeast  culture 
no  fermentation  takes  place.  The  analogy  is  obvious;  the 
fluid  in  the  first  instance  corresponds  with  an  individual 
susceptible  to  the  disease,  the  inoculated  yeast  to  the  con- 
tagion from  a  case  of  transmissible  disease,  the  fermentation 
to  the  illness  with  fever,  etc.,  which  constitutes  the  disease, 
the  returning  clearness  of  the  fluid  to  the  recovery,  and  like 
the  fermenting  fluid  the  individual  is  not  susceptible  to  a  new 
attack  of  the  disease.  It  will  be  observed  that  during  the 
process  both  the  yeast  and  the  material  which  produced  the 
disease  have  enormously  increased.  Fermentation  of  immense 
quantities  of  fluid  could  be  produced  by  the  sediment  of 
yeast  cells  at  the  bottom  of  the  vessel  and  a  single  case  of 
smallpox  would  be  capable  of  infecting  multitudes. 


DISEASE  AND   ITS   CAUSES        109 

proved  that  a  disease  of  cattle  called  anthrax  was 
due  to  a  species  of  bacteria.  What  should  be 
regarded  as  such  proof  had  been  formulated  by 
Henle  in  1840.  To  prove  that  a  certain  sort  of 
organism  when  found  associated  with  a  disease 
is  the  cause  of  the  disease,  three  things  are 
necessary : 

1.  The  organism  must  always  be  found  in  the 
diseased  animal  and  associated  with  the  changes 
produced  by  the  disease. 

2.  The  organism  so  found  must  be  grown 
outside  of  the  body  in  what  is  termed  pure  cul- 
tures, that  is,  not  associated  with  any  other 
organisms,  and  for  so  long  a  time  with  constant 
transfers  or  new  seedings  that  there  can  be  no 
admixture  of  other  products  of  the  disease  in 
the  material  in  which  it  is  grown. 

3.  The  disease  must  be  produced  by  inocu- 
lating a  susceptible  animal  with  a  small  portion 
of  such  a  culture,  and  the  organism  shown  in 
relation  to  the  lesions  so  produced. 

It  is  worth  while  to  devote  some  attention  to 
the  disease  anthrax.  This  occupies  a  unique 
position,  in  that  it  was  the  first  of  the  infec- 
tious diseases  to  be  scientifically  investigated. 
In  this  investigation  one  fact  after  another  was 
discovered  and  confirmed;  some  of  these  facts 
seemed  to  give  clearer  conceptions  of  the  disease, 
others  served  to  make  it  more  obscure;  new 
questions  arose  with  each  extension  of  knowledge; 


110       DISEASE  AND  ITS  CAUSES 

in  the  course  of  the  work  new  methods  of  investi- 
gation were  discovered;  the  sides  of  the  arch 
were  slowly  and  painfully  erected  by  the  work 
of  many  men,  and  finally  one  man  placed  the 
keystone  and  anthrax  was  for  a  long  time  the 
best  known  of  diseases.  Men  whose  reputation 
is  now  worldwide  first  became  knowna  by  their 
work  in  this  disease.  It  was  a  favorable  disease 
for  investigation,  being  a  disease  primarily  of 
cattle,  but  occasionally  appearing  in  man,  and 
the  susceptibility  of  laboratory  animals  made 
possible  experimental  study. 

Anthrax  is  a  disease  of  domestic  cattle  affecting 
particularly  bovine  cattle,  horses  and  sheep, 
swine  more  rarely.  The  disease  exists  in  practi- 
cally all  countries  and  has  caused  great  economic 
losses.  There  are  no  characteristic  symptoms 
of  the  disease;  the  affected  cattle  have  high  fever, 
refuse  to  eat,  their  pulse  and  respiration  are 
rapid,  they  become  progressively  weaker,  un- 
able to  walk  and  finally  fall.  The  disease  lasts 
a  variable  time;  in  the  most  acute  cases  animals 
may  die  in  less  than  twenty-four  hours,  or  the 
disease  may  last  ten  or  fourteen  days;  recovery 
from  the  disease  is  rare  and  treatment  has  no 
effect.  It  does  not  appear  in  the  form  of  epi- 
demics, but  single  cases  appear  frequently  or 
rarely,  and  there  is  seemingly  no  extension  from 
case  to  case,  animals  in  adjoining  stalls  to  the  sick 
are  not  more  prone  to  infection  than  others  of 


DISEASE  AND   ITS  CAUSES        111 

the  herd.  On  examination  after  death  the  blood 
is  dark  and  fluid,  the  spleen  is  greatly  enlarged 
(one  of  the  names  of  the  disease  "splenic  fever" 
indicates  the  relation  to  the  spleen)  and  there  is 
often  bloody  fluid  in  the  tissues. 

Where  the  disease  is  prevalent  there  are  numbers 
of  human  cases.  Only  those  become  infected  who 
come  into  close  relations  with  cattle,  the  infection 
most  commonly  taking  place  from  small  wounds 
or  scratches  made  in  skinning  dead  cattle  or  in 
handling  hides.  The  wool  of  sheep  who  die  of 
the  disease  finds  its  way  into  commerce,  and  those 
employed  in  handling  the  wool  have  a  form  of 
anthrax  known  as  wool-sorters'  disease  in  which 
lesions  are  found  in  the  lungs,  the  organisms 
being  mingled  with  the  wool  dust  and  inspired. 
In  Boston  occasional  cases  of  anthrax  appear  in 
teamsters  who  are  employed  in  handling  and 
carrying  hides.  The  disease  in  man  is  not  so 
fatal  as  in  cattle,  for  it  remains  local  for  a  time 
at  the  site  of  infection,  and  this  local  disease  can 
be  successfully  treated. 

The  beginning  of  our  knowledge  of  the  cause 
dates  from  1851,  when  small  rod-shaped  bodies 
(Fig.  17)  were  found  in  the  blood  of  the  affected 
cattle,  and  by  the  work  of  a  number  of  observers 
it  was  established  that  these  bodies  were  con- 
stantly present.  Nothing  was  known  of  their 
nature;  some  held  that  they  were  living  organ- 
isms,   others    that    they    were    formed    in    the 


112       DISEASE  AND  ITS  CAUSES 

body  as  a  result  of  the  disease.  Next  the 
causal  relation  of  these  bodies  wdth  the  disease 
was  shown  and  in  several  ways.  The  disease 
could  be  caused  in  other  cattle  by  injecting 
blood  containing  the  rods  beneath  the  skin, 
certainly  no  proof,  for  the  blood  might  have 
contained  in  addition  to  the  rods  something 
which  was  the  real  cause  of  the  disease.  Next 
it  was  shown  that  the  blood  of  the  unborn  calf 
of  a  cow  who  died  of  the  disease  did  not  con- 
tain the  rods,  and  the  disease  could  not  be 
produced  by  inoculating  with  the  calf's  blood 
although  the  blood  of  the  mother  was  infectious. 
This  was  a  very  strong  indication  that  the  rods 
were  the  cause;  the  maternal  and  foetal  blood 
are  separated  by  a  membrane  through  which 
fluids  and  substances  in  solution  pass;  but 
insoluble  substances,  even  when  very  minutely 
subdivided,  do  not  pass  the  membrane.  If  the 
cause  were  a  poison  in  solution,  the  foetal  blood 
would  have  been  as  toxic  as  the  maternal.  The 
blood  of  infected  cattle  was  filtered  through 
filters  made  of  unbaked  porcelain  and  having 
very  fine  pores  which  allowed  only  the  blood 
fluid  to  pass,  holding  back  both  the  blood  cor- 
puscles and  the  rods,  and  such  filtered  blood  was 
found  to  be  innocuous.  It  was  further  shown 
that  the  rods  increased  enormously  in  number  in 
the  infected  animal,  for  the  blood  contained  them 
in  great  numbers  when  but  a  fraction  of  a  drop 


DISEASE  AND   ITS  CAUSES        113 

was  used  for  inoculation.  Attempts  were  also 
made  with  a  greater  or  less  degree  of  success  to 
grow  the  rod  shaped  organisms  or  bacilli  in  vari- 
ous fluids,  and  the  characteristic  disease  was  pro- 
duced by  inoculating  animals  with  these  cultures; 
but  it  remained  for  Koch,  1878,  who  was  at  that 
time  an  obscure  young  country  physician,  to  show 
the  life  history  of  the  organism  and  to  clear  up 
the  obscurity  of  the  disease.  Up  to  that  time, 
although  it  had  been  shown  that  the  rods  or  bacilli 
contained  in  the  blood  were  living  organisms  and 
the  cause  of  the  disease,  this  did  not  explain  the 
mode  of  infection ;  how  the  organisms  contained  in 
the  blood  passed  to  another  animal,  why  the 
disease  occurred  on  certain  farms  and  the  adjoin- 
ing farms,  particularly  if  they  lay  higher,  were  free. 
Koch  showed  that  in  the  cultures  the  organisms 
grew  out  into  long  interlacing  threads,  and  that 
in  these  threads  spores  which  were  very  difficult  to 
destroy  developed  at  intervals;  that  the  organ- 
isms grew  easily  in  bouillon,  in  milk,  in  blood, 
and  even  in  an  infusion  of  hay  made  by  soaking 
this  in  water.  This  explained,  what  had  been 
an  enigma  before,  how  the  fields  became  sources 
of  infection.  The  infection  did  not  spread  from 
animal  to  animal  by  contact,  but  infection  took 
place  from  eating  grass  or  hay  which  contained 
either  the  bacilli  or  their  spores.  When  a  dead 
animal  was  skinned  on  the  field,  the  bacilli  con- 
tained in  the  blood  escaped  and  became  mingled 


114       DISEASE  AND  ITS  CAUSES 

with  the  various  fluids  which  flowed  from  the 
body  and  in  which  they  grew  and  developed 
spores.  It  was  shown  by  Pasteur  that  even  when 
a  carcass  was  buried  the  earthworms  brought 
spores  developed  in  the  body  to  the  surface  and 
deposited  them  in  their  casts,  and  in  this  way  also 
the  fields  became  infected.  From  such  a  spot  of 
infected  earth  the  spores  could  be  washed  by  the 
rains  over  greater  areas  and  would  find  opportunity 
to  develop  further  and  form  new  spores  in  puddles 
of  water  left  on  the  fields,  which  became  a  culture 
medium  by  the  soaking  of  the  dead  grass.  The 
contamination  of  the  fields  was  also  brought  about 
by  spreading  over  them  the  accumulations  of 
stable  manure  which  contained  the  discharges  of 
the  sick  cattle.  The  tendency  of  the  disease  to 
extend  to  lower-lying  adjacent  fields  was  due  to 
the  spores  being  washed  from  the  upper  fields  to 
the  lower  by  the  spring  freshets.  Meanwhile 
Pasteur  had  discovered  that  by  growing  the  organ- 
isms at  higher  temperatures  than  the  animal  body, 
it  was  possible  to  attenuate  the  virulence  of  the 
bacilli  so  that  inoculations  with  these  produced 
a  mild  form  of  the  disease  which  rendered  the  in- 
oculated animals  immune  to  the  fatal  disease. 
The  description  of  Pasteur's  work  on  the  disease 
as  given  in  the  account  of  his  life  by  his  son-in- 
law  is  fascinating. 

Hides  and  wool  taken  from  dead  animals  in- 
variably contained  the  spores  which  could  pass 


DISEASE  AND   ITS  CAUSES        115 

unharmed  through  some  of  the  curing  processes, 
and  were  responsible  for  some  of  the  cases  in 
man.  Owing  to  the  introduction  of  regulations 
which  were  based  on  the  knowledge  of  the  cause 
of  the  disease  and  the  life  history  of  the  organism, 
together  with  the  prophylactic  inoculation  de- 
vised by  Pasteur,  the  incidence  of  the  disease 
has  been  very  greatly  lessened.  Looking  at  the 
matter  from  the  lowest  point  of  view,  the  money 
which  has  been  saved  by  the  control  of  the  disease, 
as  shown  in  its  decline,  has  been  many  times  the 
cost  of  all  the  work  of  the  investigations  which 
made  the  control  possible.  It  is  a  greater  satis- 
faction to  know  that  many  human  lives  have  been 
saved,  and  that  small  farmers  and  shepherds  have 
been  the  chief  sharers  in  the  economic  benefits. 
The  indirect  benefits,  however,  which  have  re- 
sulted from  the  application  of  the  knowledge  of 
this  disease,  and  the  methods  of  investigation  de- 
veloped here,  to  the  study  of  the  infections  more 
peculiar  to  man,  are  very  much  greater. 


CHAPTER  VI 

Classification  op  the  Organisms  which  cause  Disease. 
—  Bacteria  :  Size,  Shape,  Structure,  Capacity  for 
Growth,  Multiplication  and  Spore  Formation.  — 
The  Artificial  Cultivation  of  Bacteria.  —  The  Im- 
portance of  Bacteria  in  Nature.  —  Variations  in 
Bacteria.  —  Saprophytic  and  Parasitic  Forms.  — 
Protozoa.  —  Structure  more  complicated  than  that 
OF  Bacteria.  —  Distribution  in  Nature.  —  Growth 
AND  Multiplication.  —  Conjugation  and  Sexual  Re- 
production. —  Spore  Formation.  —  The  Necessity  for 
A  Fluid  Environment.  —  The  Food  of  Protozoa.  — 
Parasitism.  —  The  Ultra-microscopic  or  Filter.'VBLe 
Organisms.  —  The  Limitation  of  the  Microscope.  — 
Porcelain  Filters  to  separate  Organisms  from  a 
Fluid.  —  Foot  and  Mouth  Disease  produced  by  an 
Ultra-microscopic  Organism.  —  Other  Diseases  so 
produced.  —  Do  New  Diseases  appear? 

The  living  organisms  which  cause  the  infectious 
diseases  are  classified  under  bacteria,  protozoa, 
yeasts,  moulds,  and  ultra-microscopic  organisms. 
It  is  necessary  to  place  in  a  separate  class  the 
organisms  whose  existence  is  known,  but  which 
are  not  visible  under  the  highest  powers  of  the 
microscope,  and  have  not  been  classified.  The 
yeasts  and  moulds  play  a  minor  part  in  the  pro- 
duction of  disease  and  cannot  be  considered  in 
the  necessary  limitation  of  space. 

The  bacteria  (Fig.  17)  are  unicellular  organ- 
isms and  vary  greatly  in  size,  shape  and  capacity 

116 


DISEASE  AND   ITS   CAUSES        117 

of  growth.  The  smallest  of  the  pathogenic  or 
disease-producing  bacteria  is  the  influenza  ba- 
cillus, 1/51000  of  an  inch  in  length  and  1/102000 


a 


*n"<:' 


Fig.  17.  —  Various  forms  op  bacteria,  a,  b,  c,  d.  Round 
bacteria  or  cocci:  (a)  Staphylococci,  orj^anisms  which  occur 
in  groups  and  a  common  cause  of  boils;  {b)  streptococci, 
organisms  which  occur  in  chains  and  produce  erysipelas 
and  more  severe  forms  of  inflammation;  (c)  diplococci,  or 
paired  organisms  with  a  capsule,  which  cause  acute  pneu- 
monia; {d)  gonococci,  with  the  opposed  surfaces  flattened, 
which  cause  gonorrhoea,  e,  f,  g,  h.  Rod-shaped  bacteria  or 
bacilli:  (e)  diphtheria  bacilli;  (/)  tubercle  bacilli;  (^)  anthrax 
bacilli;  {h)  the  same  bacilli  in  cultures  and  producing  spores; 
a  small  group  of  spores  is  shown,  (z)  Cholera  spirilla\  {j) 
Typhoid  bacilli,  {k)  Tetanus  bacillus;  i,  j,  k  are  actively 
motile,  motion  being  effected  by  the  small  attached  threads. 
(/)  The  screw-shaped  spirochite  which  is  the  cause  of  syphilis. 


of  an  inch  in  thickness;  and  among  the  largest 
is  a  bacillus  causing  an  animal  disease  which  is 
1/2000  of  an  inch  in  length  and  1/25000  of  an 


118        DISEASE  AND   ITS  CAUSES 

inch  in  diameter.  Among  the  free-Hving  non- 
pathogenic forms  much  larger  examples  are  found. 
In  shape  bacteria  are  round,  or  rod-shaped,  or 
spiral;  the  round  forms  are  called  micrococci,  the 
rod-shaped  bacilli  and  the  spiral  forms  are  called 
spirilli.  A  clearer  idea  of  the  size  is  possibly 
given  by  the  calculation  that  a  drop  of  water 
would  contain  one  billion  micrococci  of  the  usual 
size.  Their  structure  in  a  general  way  conforms 
with  that  of  other  cells.  On  the  outside  is  a  cell 
membrane  which  encloses  cytoplasm  and  nucleus; 
the  latter,  however,  is  not  in  a  single  mass,  but 
the  nuclear  material  is  distributed  through  the 
cell.  Many  of  the  bacteria  have  the  power  of 
motion,  this  being  effected  by  small  hair-like 
api>endages  or  flagellse  which  may  be  numerous, 
projecting  from  all  parts  of  the  organisms  or  from 
one  or  both  ends,  the  movement  being  produced  by 
rapid  lashing  of  these  hairs.  A  bacterium  grows 
until  it  attains  the  size  of  the  species,  when  it 
divides  by  simple  cleavage  at  right  angles  to  the 
long  axis  forming  two  individuals.  In  some  of 
the  spherical  forms  division  takes  place  alter- 
nately in  two  planes,  and  not  infrequently  the 
single  individuals  adhere,  forming  figures  of  long 
threads  or  chains  or  double  forms.  The  rate  of 
growth  varies  with  the  species  and  with  the 
environment,  and  under  the  best  conditions  may 
be  very  rapid.  A  generation,  that  is,  the  interval 
between  divisions,  has  been  seen  to  take  place  in 


DISEASE  AND  ITS  CAUSES        119 

twenty  minutes.  At  this  rate  of  growth  from  a 
single  cholera  bacillus  sixteen  quadrillion  might 
arise  in  a  single  day.  Such  a  rate  of  growth  is 
extremely  improbable  under  either  natural  or 
artificial  conditions,  both  from  lack  of  food  and 
from  the  accumulation  in  the  fluid  of  waste  pro- 
ducts which  check  growth.  Many  species  of 
bacteria  in  addition  to  this  simple  mode  of  multi- 
plication form  spores  which  are  in  a  way  analogous 
to  the  seeds  of  higher  plants  and  are  much  more 
resistant  than  the  simple  or  vegetative  forms;  they 
endure  boiling  water  and  even  higher  degrees  of 
dry  heat  for  a  considerable  time  before  they  are 
destroyed.  When  these  spores  are  placed  in 
conditions  favorable  for  bacterial  life,  the  bac- 
terial cells  grow  out  from  them  and  the  usual 
mode  of  multiplication  continues.  This  capacity 
for  spore  formation  is  of  great  importance,  and 
until  it  was  discovered  by  Cohn  in  1876,  many 
of  the  conditions  of  disease  and  putrefaction 
could  not  be  explained.  Spores,  as  the  seeds  of 
plants,  often  seem  to  be  produced  when  the 
conditions  are  unfavorable ;  the  bacterium 
then  changes  into  this  form,  which  under  natural 
conditions  is  almost  indestructible  and  awaits 
better  days. 

The  bacteria  are  divided  into  species,  the  classi- 
fication being  based  on  their  forms,  on  the  mode  of 
growth,  the  various  substances  which  they  produce 
and  their  capacity  for  producing  disease.    The  dif- 


120       DISEASE  AND  ITS  CAUSES 

ferentiation  of  species  in  bacteria  is  based  chiefly 
upon  their  properties,  there  being  too  little  dif- 
ference in  form  and  size  to  distinguish  species. 
The  introduction  of  methods  of  culture  was  fol- 
lowed by  an  immediate  advance  of  our  knowledge 
concerning  them.  This  method  consists  in  the 
use  of  fluid  and  solid  substances  which  contain  the 
necessary  salts  and  other  ingredients  for  their 
food,  and  in  or  on  which  they  are  planted.  The 
use  of  a  solid  or  gelatinous  medium  for  growth  has 
greatly  facilitated  the  separation  of  single  species 
from  a  mixture  of  bacteria;  a  culture  fluid  contain- 
ing suflficient  gelatine  to  render  it  solid  when  cooled 
is  sown  with  the  bacteria  to  be  tested  by  placing 
in  it  while  warm  and  fluid,  a  small  portion  of 
material  containing  the  bacteria,  and  after  being 
thoroughly  mixed  the  fluid  is  poured  on  a  glass 
plate  and  allowed  to  cool.  The  bacteria  are  in 
this  way  separated,  and  each  by  its  growth  forms 
a  single  colony  which  can  be  further  tested.  It 
is  self-evident  that  all  culture  material  must  be 
sterilized  by  heat  before  using,  and  in  the  manipu- 
lations care  must  be  exercised  to  avoid  contami- 
nation from  the  air.  The  refraction  index  of  the 
bacterial  cell  is  so  slight  that  the  microscopic 
study  is  facilitated  or  made  possible  by  staining 
them  with  various  aniline  dyes.  Owing  to 
differences  in  the  cell  material  the  different 
species  of  bacteria  show  differences  in  the  facility 
with  which  they  take  the  color  and  the  tenacity 


DISEASE  AND   ITS  CAUSES        121 

with  which  they  retain  it,  and  this  also  forms 
a  means  of  species  differentiation.  The  inter- 
relation of  science  is  well  shown  in  this,  for  it 
was  the  discovery  of  the  aniline  dyes  in  the  latter 
half  of  the  nineteenth  century  which  made  the 
fruitful  study  of  bacteria  possible. 

From  the  simplicity  of  structure  it  is  not 
improbable  that  the  bacteria  are  among  the 
oldest  forms  of  life,  and  all  life  has  become  adapted 
to  their  presence.  They  are  of  universal  distribu- 
tion; they  play  such  an  important  part  in  the 
inter-relations  of  living  things  that  it  is  probable 
life  could  not  continue  without  them,  at  least  not 
in  the  present  way.  They  form  important  food 
for  other  unicellular  organisms  which  are  im- 
portant links  in  the  chain;  they  are  the  agents  of 
decomposition,  by  which  the  complex  substances 
of  living  things  are  reduced  to  elementary  sub- 
stances and  made  available  for  use;  without  them 
plant  life  would  be  impossible,  for  it  is  by  their 
instrumentality  that  material  in  the  soil  is  so 
changed  as  to  be  available  as  plant  food;  by 
their  action  many  of  the  important  foods  of  man, 
often  those  especially  delectable,  are  produced; 
they  are  constantly  with  us  on  all  the  surfaces 
of  the  body;  masses  live  on  the  intestinal  surfaces 
and  the  excrement  is  largely  composed  of  bac- 
teria. It  has  been  said  that  life  would  be  impos- 
sible without  bacteria,  for  the  accumulation  of 
the  carcasses  of  all  animals  which  have  died  would 


122       DISEASE  AND  ITS  CAUSES 

so  encumber  the  earth  as  to  prevent  its  use;  but 
the  folly  of  such  speculation  is  shown  by  the  fact 
that  animals  would  not  have  been  there  without 
bacteria.  It  has  been  shown,  however,  that  the 
presence  of  bacteria  in  the  intestine  of  the  higher 
animals  is  not  essential  for  life.  The  coldest 
parts  of  the  ocean  are  free  from  those  forms 
which  live  in  the  intestines,  and  fish  and  birds 
inhabiting  these  regions  have  been  found  free 
from  bacteria;  it  has  also  been  found  possible 
to  remove  small  animals  from  their  mother  by 
Caesarian  section  and  to  rear  them  for  a  few 
weeks  on  sterilized  food,  showing  that  digestion 
and  nutrition  may  go  on  without  bacteria. 

Certain  species  of  bacteria  are  aerobic,  that  is, 
they  need  free  oxygen  for  their  growth;  others  are 
anaerobic  and  will  not  grow  in  the  presence  of 
oxygen.  Most  of  the  bacteria  which  produce 
disease  are  facultative,  that  is,  they  grow  either 
with  or  without  oxygen;  but  certain  of  them, 
as  the  bacillus  of  tetanus,  are  anaerobic.  There 
is,  of  course,  abundance  of  oxygen  in  the  blood 
and  tissues,  but  it  is  so  combined  as  to  be  un- 
available for  the  bacteria.  Bacteria  may  further 
be  divided  into  those  which  are  saprophytic  or 
which  find  favorable  conditions  for  life  outside 
of  the  body,  and  the  parasitic.  Many  are  ex- 
clusively parasitic  or  saprophytic,  and  many  are 
facultative,  both  conditions  of  living  being  pos- 
sible.   It  has  been  found  possible  by  varying  in 


DISEASE  AND  ITS  CAUSES        123 

many  ways  the  character  of  the  culture  medium 
and  temperature  to  grow  under  artificial  con- 
ditions outside  of  the  body  most,  if  not  all,  of 
the  bacteria  which  cause  disease.  Thus,  such 
bacteria  as  tubercle  bacilli  and  the  influenza 
bacillus  can  be  cultivated,  but  they  certainly 
would  not  find  natural  conditions  which  would 
make  saprophytic  growth  possible. 

Bacteria  may  be  very  sensitive  to  the  presence 
of  certain  substances  in  the  fluid  in  which  they 
are  growing.  Growth  may  be  inhibited  by  the 
smallest  trace  of  some  of  the  metallic  salts,  as 
corrosive  sublimate,  although  the  bacteria  them- 
selves are  not  destroyed.  If  small  pieces  of  gold 
foil  be  placed  on  the  surface  of  prepared  jelly 
on  which  bacteria  have  been  planted,  no  growth 
will  take  place  in  the  vicinity  of  the  gold  foil. 

Variations  can  easily  be  produced  in  bacteria, 
but  they  do  not  tend  to  become  established. 
In  certain  of  the  bacterial  species  there  are 
strains  which  represent  slight  variations  from 
the  type  but  which  are  not  sufficient  to  consti- 
tute new  species.  If  the  environment  in  which 
bacteria  are  living  be  unusual  and  to  a  greater 
or  less  degree  unfavorable,  those  individuals  in 
the  mass  with  the  least  power  of  adaptibility 
will  perish,  those  more  resistant  and  with  greater 
adaptability  will  survive  and  propagate;  and 
the  peculiarity  being  transmitted  a  new  strain  will 
arise  characterized  by  this  adaptability.     Bac- 


124       DISEASE  AND   ITS  CAUSES 

teria  with  slight  adaptability  to  the  environment 
of  the  tissues  and  fluids  of  the  animal  body  can, 
by  repeated  inoculations,  become  so  adapted  to 
the  new  environment  as  to  be  in  a  high  degree 
pathogenic.  In  such  a  process  the  organisms 
with  the  least  power  of  adaptation  are  destroyed 
and  new  generations  are  formed  from  those  of 
greater  power  of  adaptation.  WTien  bacteria  are 
caused  to  grow  in  a  new  environment  they  may 
acquire  new  characteristics.  The  anthrax  bacilli 
find  the  optimum  conditions  for  growth  at  the 
temperature  of  the  animal  body,  but  they  will 
grow  at  temperatures  both  above  and  below  this. 
Pasteur  found  that  by  gradually  increasing  the 
temperature  they  could  be  grown  at  one  hundred 
and  ten  degrees.  When  grown  at  this  tem- 
perature they  were  no  longer  so  virulent  and 
produced  in  animals  a  mild  non-fatal  form  of 
anthrax  wh^ch  protected  the  animal  when  in- 
oculated with  the  virulent  strain.  The  well 
known  variations  in  the  character  of  disease, 
shown  in  differences  in  severity  and  ease  of  trans- 
mission, seen  in  different  years  and  in  different 
epidemics,  may  be  due  to  many  conditions,  but 
probably  variation  in  the  infecting  organisms  is 
the  most  important. 

The  protozoa,  like  the  bacteria,  are  unicellular 
organisms  and  contain  a  nucleus  as  do  all  cells. 
They  vary  in  size  from  forms  seen  with  difficulty 
under  the  highest  power  of  the  microscope  to 


DISEASE  AND   ITS   CAUSES        125 

forms  readily  seen  with  the  unaided  eye.  Their 
structure  in  general  is  more  complex  than  is  the 
structure  of  bacteria,  and  many  show  extreme 
differentiation  of  parts  of  the  single  cells,  as  a 
firm  exterior  surface  or  cuticle,  an  internal  skele- 
ton, organs  of  locomotion,  mouth  and  digestive 
organs  and  organs  of  excretion.  They  are  more 
widely  distributed  than  are  the  bacteria,  and 
found  from  pole  to  pole  in  all  oceans  and  in  all 
fresh  water.  There  are  many  modes  of  multi- 
plication, and  these  are  often  extremely  compli- 
cated. The  most  general  mode  and  one  which  is 
common  to  all  is  by  simple  division;  a  modification 
of  this  is  by  budding  in  which  projections  or  buds 
form  on  the  body  and  after  separation  become 
new  organisms.  In  other  cases  spores  form  within 
the  cell  which  become  free  and  develop  further 
into  complete  organisms.  These  simple  modes 
of  multiplication  often  alternate  in  the  same 
organism  with  sexual  differentiation  and  con- 
jugation. There  is  never  a  permanent  sexual 
differentiation,  but  the  sexual  forms  develop 
from  a  simple  and  non-sexual  organism.  Usually 
the  sexual  forms  develop  only  in  a  special  environ- 
ment; thus  the  protozoon  which  in  man  is  the 
cause  of  malaria,  multiplies  in  the  human  blood 
by  simple  division,  but  in  the  body  of  the  mos- 
quito multiplication  by  sexual  differentiation 
takes  place.  Under  no  conditions  is  multiplica- 
tion so  rapid  as  with  the  bacteria,  and  in  general 


126        DISEASE  AND   ITS   CAUSES 

the  simpler  the  form  of  organism  the  more  rapid 
is  the  multiplication.  It  is  common  to  all  of 
the  protozoa  to  develop  forms  which  have  great 
powers  of  resistance,  this  being  due  in  some 
cases  to  encystment,  in  which  condition  a  resistant 
membrane  is  formed  on  the  outside,  in  others 
to  the  production  of  spores.  A  fluid  environment 
is  essential  to  the  life  of  the  protozoa,  but  the 
resistant  forms  can  endure  long  periods  of  dryness 
or  other  unfavorable  environmental  conditions. 
The  universal  distribution  of  the  protozoa  is 
due  to  this;  the  spores  or  cysts  can  be  carried 
long  distances  by  the  wind  and  develop  into 
active  forms  when  they  reach  an  environment 
which  is  favorable.  Their  distribution  in  water 
depends  upon  the  amount  of  organic  material 
this  contains.  In  pure  drinking  water  there 
may  be  very  few,  but  in  stagnant  water  they  are 
very  numerous,  living  not  on  the  organic  material 
in  solution  in  this,  but  on  the  bacteria  which 
find  in  such  fluid  favorable  conditions  for  exist- 
ence. The  food  of  protozoa  consists  chiefly  of 
other  organisms,  particularly  bacteria,  and  they 
are  classed  with  the  animals.  The  protozoa  are 
the  most  widely  distributed  and  the  most  uni- 
versal of  the  parasites.  The  infectious  diseases 
which  they  produce  in  man,  although  among 
the  most  serious  are  less  in  number  than 
those  produced  by  bacteria.  So  marked  is  the 
tendency  to  parasitism  that  they  are  often  para- 


DISEASE  AND   ITS  CAUSES        127 

sitic  for  each  other,  smaller  forms  entering  into 
and  living  upon  the  larger.  Variation  does  not 
seem  to  be  so  marked  in  the  protozoa  as  in  the 
bacteria,  though  this  is  possibly  due  to  our  greater 
ignorance  of  them  as  a  class.  We  are  not  able, 
except  in  rare  instances,  to  grow  them  in  pure 
culture,  and  study  innumerable  generations  under 
changes  in  the  environment,  as  the  bacteria  have 
been  studied. 

If  we  regard  the  living  things  on  earth  from 
the  narrow  point  of  view  as  to  whether  they  are 
necessary  or  useless  or  hostile  to  man,  the  pro- 
tozoa must  be  regarded  as  about  the  least  useful 
members  of  the  biological  society.  It  is  very 
possible  that  such  a  conclusion  is  due  to  ignorance; 
so  closely  are  all  living  things  united,  so  dependent 
is  one  form  of  cell  activity  upon  other  forms  that 
it  is  impossible  to  foretell  the  result  of  the 
removal  of  a  link.  The  protozoa  do  not  seem 
to  be  as  necessary  for  the  life  of  man  as  are  the 
bacteria;  they  produce  many  of  the  diseases  of 
man,  many  of  the  diseases  of  animals  on  which 
man  depends  for  food;  they  cause  great  destruc- 
tion in  plant  life,  and  in  the  soil  they  feed  upon 
the  useful  bacteria.  It  is  well  to  remember, 
however,  that  fifty  years  ago  several  of  the  organs 
of  the  body  whose  activity  we  now  recognize 
as  furnishing  substances  necessary  for  life  were 
regarded  as  useless  members  and,  since  they 
became  the  seat  of  tumors,  as  dangerous  mem- 


128       DISEASE  AND  ITS  CAUSES 

bers  of  the  body.  The  only  organ  which  now 
seems  to  come  into  such  a  class  is  the  vermiform 
appendix,  and  its  lowly  position  among  organs 
is  due  merely  to  an  unhappy  accident  of  de- 
velopment. 

The  class  of  organisms  known  as  the  filterable 
viruses  or  the  ultra-microscopic  or  the  invisible 
organisms  have  a  special  interest  in  many  ways. 
The  limitation  in  the  power  of  the  microscope 
for  the  study  of  minute  objects  is  due  not  to  a 
defect  in  the  instrument  but  to  the  length  of 
the  wave  of  light.  It  is  impossible  to  see  clearly 
under  the  microscope  using  white  light,  objects 
which  are  smaller  in  diameter  than  the  length 
of  the  wave  which  gives  a  limit  of  0.5  fi,  or  1/125,- 
000  of  an  inch.  By  using  waves  of  shorter  length, 
as  the  ultra-violet  light,  objects  of  0.1  fi.  or 
1/250000  of  an  inch  can  be  seen;  but  as  these 
methods  depend  upon  photography  for  the 
demonstration  of  the  object  the  study  is  diffi- 
cult. The  presence  of  objects  still  smaller  than 
0.1  m.  can  be  detected  in  a  fluid  by  the  use  of 
the  dark  field  illumination  and  the  ultra-micro- 
scope, the  principle  of  which  is  the  direction  of 
a  powerful  oblique  ray  of  light  into  the  field  of 
the  microscope.  The  objects  are  not  visible  as 
such,  but  the  dispersion  of  the  light  by  their 
presence  is  seen. 

The  demonstration  that  infectious  diseases 
were  produced  by  organisms  so  small  as  to  be 


DISEASE  AND   ITS  CAUSES        129 

beyond  demonstration  with  the  best  micro- 
scopes was  made  possible  by  showing,  that  some 
fluid  from  a  diseased  animal  was  infectious; 
and  capable  of  producing  the  disease  when  in- 
oculated into  a  susceptible  animal.  The  fluid 
was  then  filtered  through  porcelain  filters 
which  were  known  to  hold  back  all  objects  of 
the  size  of  the  smallest  bacteria  and  the  disease 
produced  by  inoculating  with  the  clear  filtrate. 
There  are  a  number  of  such  filters  of  different 
degrees  of  porosity  manufactured,  and  they  are 
often  used  to  procure  pure  water  for  drinking, 
for  which  use  they  are  more  or  less,  generally 
however,  less  efficacious.  The  filter  has  the  form 
of  a  hollow  cylinder  and  the  liquid  to  be  filtered 
is  forced  through  it  under  pressure.  For  domestic 
use  the  filter  is  attached  by  its  open  end  to  the 
water  tap  and  the  pressure  from  the  mains  forces 
the  water  through  it.  In  laboratory  uses,  denser 
filters  of  smaller  diameters  are  used,  and  the 
filter  is  surrounded  by  the  fluid  to  be  tested. 
The  open  end  of  the  filter  passes  into  a  vessel 
from  which  the  air  is  exhausted  and  filtration 
takes  place  from  without  inward.  The  test  of 
the  effectiveness  of  the  filter  is  made  by  adding 
to  the  filtering  fluid  some  very  minute  and 
easily  recognizable  bacteria  and  testing  the 
filtrate  for  their  presence.  These  filters  have 
been  studied  microscopically  by  grinding  very 
thin  sections  and  measuring  the  diameter  of  the 


130       DISEASE  AND  ITS  CAUSES 

spaces  in  the  material.  These  are  very  numerous, 
and  from  1/25000  to  1/1000  of  an  inch  in 
diameter,  spaces  which  would  allow  bacteria 
to  pass  through,  but  they  are  held  back  by  the 
very  jfine  openings  between  the  spaces  and  by 
the  tortuosity  of  the  intercommunications.  When 
the  coarser  of  such  filters  have  been  long  in 
domestic  service  in  filtering  drinking  water,  bac- 
teria may  grow  in  and  through  them  giving 
greater  bacterial  content  to  the  supposed  bac- 
teria-free filtrate  than  in  the  filtering  water. 

That  an  animal  disease  was  due  to  such  a 
minute  and  filterable  organism  was  first  shown 
by  Loeffler  in  1898  for  the  foot  and  mouth  disease 
of  cattle.  This  is  one  of  the  most  infectious  and 
easily  communicable  diseases.  The  lesions  of 
the  disease  take  the  form  of  blisters  which  form 
on  the  lips  and  feet  and  in  the  mouths  of  cattle, 
and  inoculation  with  minute  quantities  of  the 
fluid  in  the  blisters  produces  the  disease.  Loeffler 
filtered  the  fluid  through  porcelain  filters,  hoping 
to  obtain  a  material  which  inoculated  into  other 
cattle  would  render  them  immune,  and  to  his 
surprise  found  that  the  typical  disease  was  pro- 
duced by  inoculating  with  the  filtrate.  Natu- 
rally the  first  idea  was  that  the  disease  was  caused 
by  some  soluble  poison  and  not  by  a  living  organ- 
ism, but  this  was  disproved  in  a  number  of  ways. 
The  most  powerful  poison  known  is  obtained 
from  cultures  of  the  tetanus  bacillus  of  which 


DISEASE  AND   ITS  CAUSES        131 

0.000,000,1  of  a  gram  (one  gram  is  15.43  grains) 
kills  a  mouse,  or  one  gram  kills  ten  million 
mice.  Loeffler  found  that  1/30  gram  of  the  con- 
tents of  the  vesicles  killed  a  calf  of  two  hundred 
kilograms  weight,  and  assuming  that  the  essen- 
tial poison  was  present  in  the  fluid  in  one  part  to 
five  hundred  it  would  be  several  hundred  times 
more  powerful  than  the  tetanus  poison.  Further, 
the  disease  produced  by  inoculation  of  the  filtrate 
was  itself  inoculable  and  could  be  transmitted 
from  animal  to  animal.  It  was  also  found  that 
when  the  virus  was  filtered  several  times  it  ceased 
to  be  itioculable,  showing  that  each  time  the 
fluid  was  passed  through  the  filter  some  of  the 
minute  organisms  contained  in  it  were  held  back. 
It  is  not  known  whether  these  organisms  belong 
to  the  bacteria  or  protozoa,  and  naturally  noth- 
ing is  known  as  to  their  form,  size  and  structure. 
Up  to  the  present  about  twenty  diseases  are 
known  to  be  due  to  a  filterable  virus,  and  among 
these  are  some  of  the  most  important  for  animals 
and  for  man.  Among  the  human  diseases,  yellow 
fever,  poliomyelitis,  and  dengue  are  so  produced; 
of  the  animal  diseases  in  addition  to  foot  and 
mouth  disease,  pleuropneumonia,  cattle  plague, 
African  horse  sickness,  several  diseases  of  fowls 
and  the  mosaic  disease  of  the  tobacco  plant 
have  all  been  shown  to  be  due  to  a  filterable 
virus.  Of  these  organisms  the  largest  is  that 
which  produces  pleuropneumonia  in  cattle,  and 


132       DISEASE  AND  ITS  CAUSES 

this  alone  has  been  cultivated.  It  gives  a  slight 
opacity  to  the  culture  fluids,  and  when  magnified 
two  thousand  diameters  appears  as  a  minute 
spiral  or  round  or  stellate  organism  having  a 
variety  of  forms.  Its  size  is  such  that  it  passes 
the  coarse,  but  is  held  back  by  the  finer,  filters 
and  it  is  possible  that  this  does  not  belong  to 
the  same  class  with  the  others.^  The  diseases  pro- 
duced by  the  filterable  viruses  taken  as  a  class 
show  much  similarity.  They  run  an  acute  course, 
are  severe,  and  the  immunity  produced  by  the 
attack  endures  for  a  long  time. 

Considered  in  its  biological  relations,  infection 
is  the  adaptation  of  an  organism  to  the  environ- 
ment which  the  body  of  the  host  offers.  It  is 
rather  singular  that  variations  in  organisms 
represented  by  such  adaptation  do  not  more 
frequently  arise,  in  which  case  new  diseases 
would  frequently  occur.  It  cannot  be  denied 
that  new  diseases  appear,  but  there  is  no  certain 
evidence  that  they  do,  and  there  is  equally  no 
evidence  that  diseases  disappear.  From  the 
meagre  descriptions  of  diseases,  usually  of  the 
epidemic  type,  which  have  come  down  to  us  from 
the  past,  it  is  difficult  to  recognize  many  of  the 
diseases  described.  The  single  diseases  are 
recognized  by  comparing  the  causes,  the  lesions 

*  Flexner  has  recently  succeeded  in  isolating  and  cultivat- 
ing the  organism  of  poliomyelitis,  but  the  organism  is  ao 
small  that  its  classification  is  not  possible. 


DISEASE  AND   ITS   CAUSES        133 

and  the  symptoms  with  those  of  other  dis- 
eases, and  new  diseases  are  constantly  being 
separated  off  from  other  diseases  having  more 
or  less  common  features.  Many  new  diseases 
have  been  recognized  and  named,  but  it  is 
always  more  than  probable  that  previously  they 
were  confounded  with  other  diseases.  Small- 
pox is  such  a  characteristic  disease  that  one 
would  think  it  would  have  been  recognized  as 
an  entity  from  the  beginning,  but  although 
the  description  of  some  of  the  epidemics  in 
remote  times  conform  more  or  less  to  the 
disease  as  we  know  it,  the  first  accurate  descrip- 
tion is  in  the  eighth  century  by  the  Arabian 
physician  Rhazes.  Cerebro-spinal  meningitis 
was  not  recognized  as  a  separate  disease  until 
1803,  diphtheria  not  until  1826,  and  the  sepa- 
ration between  typhoid  and  typhus  fever  was  not 
made  before  1840.  Nor  is  it  sure  that  any  dis- 
eases have  disappeared,  although  there  seems  to 
have  been  a  change  in  the  character  of  many. 
It  is  diflficult  to  reconcile  leprosy  as  it  appears 
now  with  the  universal  horror  felt  towards  it, 
due  to  the  persistence  of  the  old  traditions.  It 
is  possible,  however,  that  the  disease  has  not 
changed  its  character,  but  that  such  diseases  as 
smallpox,  syphilis,  and  certain  forms  of  tuber- 
culosis were  formerly  confounded  with  leprosy, 
thus  giving  a  false  idea  of  its  prevalence. 

In  certain  cases  the  adaptation  of  the  organism 


134        DISEASE  AND   ITS  CAUSES 

is  for  a  narrow  environment;  for  example,  the 
parasitism  jnay  extend  to  a  simple  species  only,  in 
others  the  adaptation  may  extend  to  a  number  of 
genera.  In  certain  cases  the  adaptation  is  mutual, 
extending  to  both  parasite  and  host  and  resulting 
in  symbiosis,  and  this  condition  may  be  advanta- 
geous for  both.  Certain  of  the  protozoa  harbor 
within  them  cells  of  algse  utilizing  to  their  own 
advantage  the  green  chlorophil  of  the  algae  in 
obtaining  energy  from  sunlight  and  in  turn 
giving  sustenance  to  the  algse.  Although  the 
algae  are  useful  guests,  when  they  become  too 
numerous  the  protozoan  devours  them.  It  is 
evident  that  symbiosis  is  the  most  favorable 
condition  for  the  existence  of  the  parasite,  and 
an  injurious  action  exerted  by  the  parasite  on 
the  host  unfavorable.  The  death  of  the  host 
is  an  unfortunate  incident  from  the  parasite's 
point  of  view  in  that  it  is  deprived  of  habita- 
tion and  food  supply,  being  placed  in  the  same 
unfortunate  situation  as  may  befall  a  social  para- 
site by  the  death  of  his  host. 


CHAPTER  VII 

The  Nature  op  Infection.  —  The  Invasion  op  the  Body 
FROM  ITS  Surfaces.  —  The  Protection  op  these  Sur- 
faces. —  Can  Bacteria  pass  through  an  Uninjured 
Surface.  —  Infection  from  Wounds.  —  The  Wounds 
IN  Modern  Warfare  less  Prone  to  Infection.  —  The 
Relation  op  Tetanus  to  Wounds  caused  by  the  Toy 
Pistol.  —  The  Primary  Focus  or  Atrium  of  Infec- 
tion. —  The  Dissemination  of  Bacteria  in  the  Body. 
—  The  Different  Degrees  of  Resistance  to  Bacteria 

shown  by  the  various  organs. mode  of  action  op 

Bacteria.  —  Toxin  Production.  —  The  Resistance  op 
THE  Body  to  Bacteria.  —  Conflict  between  Parasite 
AND  Host.  —  On  Both  Sides  Means  of  Offense  and 
Defense.  —  Phagocytosis. — The  Destruction  of  Bac- 
teria by  the  Blood.  —  The  Toxic  Bacterial  Dis- 
eases. —  Toxin  and  Antitoxin.  —  Immunity.  —  The 
Theory  op  Ehrlich. 

As  has  been  said,  infection  consists  in  the 
injury  of  the  body  by  living  organisms  which 
enter  it.  The  body  is  in  relation  to  the  external 
world  by  its  surfaces  only,  and  organisms  must 
enter  it  by  some  one  of  these  surfaces.  It  is  true 
that  the  bacteria  in  the  intestine  —  either  those 
normally  present  or  unusual  varieties  —  may, 
under  certain  circumstances,  produce  substances 
which  are  injurious  when  absorbed;  but  this 
is  not  infection,  and  is  analogous  to  any  other 
sort  of  poisoning.  Each  surface  of  the  body  has 
its  own  bacterial  flora.     Organisms  live  on  the 

135 


136       DISEASE  AND  ITS  CAUSES 

surface  either  on  matter  which  is  secreted  by 
the  surface  or  they  use  up  an  inappreciable 
amount  of  body  material.  Many  of  these  bac- 
teria are  harmless,  some  are  protective,  producing 
by  their  growth  such  changes  in  the  surface  fluids 
that  these  become  hostile  to  the  existence  of 
other  and  pathogenic  forms.  The  surfaces  also 
frequently  harbor  pathogenic  organisms  which 
await  some  condition  to  arise  which  will  permit 
them  to  effect  entrance  into  the  tissues. 

The  surfaces  of  the  body  protect  from  invasion 
to  a  greater  or  less  degree.  The  skin  protects 
by  the  impervious  homy  layer  on  the  outside,  the 
external  cells  of  which  are  dead  and  constantly 
being  thrown  off.  Bacteria  are  always  found  on 
and  in  this  layer,  but  the  conditions  for  growth 
here  are  not  very  favorable  and  the  surface  is 
constantly  cleansed  by  desquamation.  The  new 
cells  to  supply  the  loss  are  produced  in  the  deepest 
layer  of  the  epidermis,  and  the  movement  of 
cells  and  fluids  takes  place  from  within  outwards. 
The  protection  is  less  perfect  about  the  hairs 
and  the  sweat  glands.  Infection  by  the  route 
of  the  sweat  glands  is,  however,  imcommon,  for 
the  sweat  is  a  fluid  unfavorable  for  bacterial 
growth  and  the  flow  acts  mechanically  in 
washing  away  organisms  which  may  have  entered 
the  ducts.  Infection  by  the  route  of  the  hair 
follicles  is  common.  There  is  no  mechanical 
cleansing  as  by  the  sweat,  the  space  around  the 


DISEASE  AND   ITS   CAUSES        137 

hair  is  large  and  the  accumulated  secretion  of 
the  hair  glands  and  the  desquamated  cells  furnish 
a  material  in  which  bacteria  may  grow.  Growing 
as  a  mass  in  this  situation,  they  may  produce 
sufficient  toxic  material  to  destroy  adjacent 
living  cells  and  thus  effect  entrance.  Infection 
from  the  eye  is  not  common,  the  surface,  though 
moist,  is  smooth;  the  eyelashes  around  the 
margin  of  the  lids  give  some  mechanical  pro- 
tection from  the  entrance  of  bacteria  contained 
in  dust,  and  the  movements  of  the  lids  and  the 
constant  and  easily  accelerated  secretion  of 
tears  act  mechanically  in  removing  foreign  sub- 
stances. It  is  possible  that  the  mechanical 
cleansing  of  the  skin  by  the  daily  bath  may  have 
some  action  in  preventing  infection. 

The  internal  surfaces  are  much  more  exposed 
to  attack  and  the  protection  is  not  so  efficient. 
The  moisture  of  these  surfaces  is  both  a  pro- 
tection and  a  source  of  danger.  It  protects  by 
favoring  the  lodgment  near  the  orifices  of  organ- 
isms which  are  in  the  inspired  air,  for  when 
bacteria  touch  a  moist  surface  they  cannot  be 
raised  from  this  and  carried  further  by  air  cur- 
rents. The  moisture  is  a  source  of  danger  in 
that  it  favors  the  growth  of  bacteria  which  lodge 
on  the  surface.  The  respiratory  surface  which 
is  most  exposed  to  infection  from  the  air  is 
further  protected  by  the  cilia,  which  are  fine 
hair-like    processes    covering    the    cells    of    the 


138        DISEASE  AND  ITS   CAUSES 

surface  and  which  by  their  constant  motion 
sweep  out  fine  particles  of  all  sorts  which  lodge 
upon  them.  The  cavity  of  the  mouth  harbors 
large  numbers  of  organisms,  many  of  them  patho- 
genic. It  forms  a  depot  from  which  bacteria  may 
pass  to  communicating  surfaces  and  infection 
from  these  may  result.  Food  particles  collect 
in  the  mouth  and  provide  culture  material,  and 
there  are  many  crypts  and  irregularities  of  surface 
which  oppose  mechanical  cleaning.  Infection 
of  the  middle  ear,  the  most  common  cause  of 
deafness,  takes  place  by  means  of  the  Eustachian 
tube  which  connects  the  cavity  of  the  ear  with 
the  mouth.  Organisms  from  the  mouth  can 
extend  into  the  various  large  salivary  glands 
by  means  of  the  ducts  and  give  rise  to  infections. 
The  tonsils,  particularly  in  children,  provide  a 
favorable  surface  for  infection.  The  mucous 
surface  extends  into  these  forming  deep  pockets 
lined  with  very  thin  epitheUum,  and  in  these 
debris  of  all  sorts  accumulates  and  provides 
material  favorable  for  bacterial  growth. 

The  lungs  at  first  sight  seem  to  oflfer  the  most 
favorable  surface  for  infection.  The  surface, 
ninety-seven  square  yards,  is  enormous;  it  is 
moist,  the  epithelial  covering  is  so  thin  as  to 
give  practically  no  mechanical  protection,  large 
amounts  of  air  constantly  pass  in  and  out,  and 
the  surface  is  in  contact  with  this.  They  are 
protected   from    infection  in  many  ways.     The 


DISEASE  AND   ITS   CAUSES        139 

tubes  or  bronchi  by  which  the  air  passes  into 
and  from  the  lungs  are  covered  with  ciHa;  the 
surface  area  of  these  tubes  constantly  enlarges  as 
they  branch,  the  sum  of  the  diameters  of  the 
small  tubes  being  many  times  greater  than  that 
of  the  windpipe,  and  this  enlargement  by  re- 
tarding the  motion  of  the  air  favors  the  lodg- 
ment of  particles  on  the  surface  whence  they 
are  removed  by  the  action  of  the  cilia.  The 
entering  air  is  also  brought  closely  in  contact  with 
a  moist  surface  at  the  narrow  opening  of  the 
larynx.  That  bacteria  and  other  foreign  sub- 
stances can  enter  the  lungs  in  spite  of  these 
guards  is  shown  not  only  by  the  infections  which 
take  place  here,  but  also  by  the  large  amount  of 
black  carbon  deposited  in  them  from  the  soot 
contained  in  the  air. 

Infection  rarely  takes  place  from  the  surface 
of  the  gullet  or  oesophagus  which  leads  from  the 
mouth  to  the  stomach.  This  is  due  to  the  smooth- 
ness of  the  surface  and  to  the  rapidity  with  which 
food  passes  over  it.  Infection  by  the  stomach 
also  is  rare,  for  this  contains  a  strong  acid  secre- 
tion which  destroys  many  of  the  bacteria  which 
are  taken  in  with  the  food.  It  is  found  impos- 
sidle  to  infect  animals  with  cholera  unless  the 
acidity  of  the  stomach  contents  be  neutralized 
by  an  alkali.  Many  organisms,  although  their 
growth  in  the  stomach  is  inhibited,  are  not 
destroyed   there   and   pass   into   the   intestines. 


140        DISEASE  AND   ITS  CAUSES 

where  the  conditions  for  infection  are  more 
favorable.  This  large  and  very  irregular  surface 
is  bathed  in  fluid  which  is  a  good  culture  medium 
and  but  a  single  layer  of  cells  covers  it.  The 
organisms  which  cause  many  of  the  infectious 
diseases  in  both  man  and  animals  find  entrance 
by  means  of  the  alimentary  canal,  as  cholera, 
dysentery,  typhoid  fever,  chicken  cholera,  hog 
cholera. 

Infection  by  the  genito-urinary  surface  is 
comparatively  rare.  The  surface  openings  are 
usually  closed,  and  the  discharge  of  urine  has  a 
mechanical  cleansing  effect.  The  wide  tube  of 
the  vagina  is  further  protected  by  a  normal 
bacterial  flora  which  produces  conditions  hostile 
to  other  and  pathogenic  bacteria.  The  most 
common  infections  are  the  sexual  diseases,  which 
are  due  to  organisms  which  find  favorable  con- 
ditions for  growth  in  and  on  the  surface  and 
which  are  conveyed  from  a  similar  surface  by 
sexual  contact. 

It  remains  a  question  whether  bacteria  can 
penetrate  an  intact  surface  producing  no  injury 
at  the  point  of  entrance  and  be  carried  by  the 
lymph  or  blood  into  internal  organs  where  they 
produce  disease.  Internal  infections  are  often 
found  with  seemingly  intact  body  surfaces,  but 
it  is  impossible  to  exclude  the  presence  of  minute 
or  microscopic  surface  injuries  by  which  the 
organisms  may  have  entered.    It  is  also  possible 


DISEASE  AND   ITS  CAUSES        141 

that   a  slight  injury  at  the  point  of  entrance 
may  heal  so  completely  as  to  leave  no  trace. 

The  chief  danger  from  wounds  is  that  their 
surfaces  may  become  infected.  Death  from 
wounds  is  due  more  frequently  to  infection  than 
to  the  actual  injury  represented  by  the  wounds. 
Much  depends  upon  the  character  of  the  wound. 
Infection  of  clean  wounds  which  are  made  by 
a  sharp  cutting  instrument  and  from  which  there 
is  abundant  haemorrhage  with  sealing  of  the  edges 
of  the  wound  by  clotted  blood,  rarely  happens. 
Typical  wounds  of  this  sort  are  often  made  in 
shaving,  and  infection  of  such  wounds  is  extraor- 
dinarily rare.  If,  with  the  wound,  pathogenic 
organisms  are  placed  in  the  tissue,  or  foreign 
substances  such  as  bits  of  clothing  are  carried 
in  with  a  bullet,  for  example,  or  if  the  instrument 
causing  the  wound  be  of  such  a  character  as  to 
produce  extensive  lacerations  of  tissue,  infection 
is  more  apt  to  occur.  The  less  frequency  of  in- 
fection in  modern  wars  is  in  part  due  to  the 
simpler  character  of  the  wounds  and  in  part  to 
the  fact  that  modern  fixed  ammunition  is  practi- 
cally free  from  germs.  The  old  spear-head,  the 
arrow,  the  cross  bow  bolt,  had  little  regard 
for  the  probabilities  of  infection.  Whether  in- 
fection follows  a  wound  depends  both  upon 
the  entry  of  pathogenic  organisms  and  upon 
these  finding  in  the  tissues  suitable  opportunities 
for  growth.     In  wounds  in  which  there  is  much 


142       DISEASE  AND  ITS  CAUSES 

laceration  of  tissue  organisms  find  the  most 
favorable  conditions  for  development.  The  very 
slight  wounds  produced  by  the  exploded  cap 
in  the  toy  pistol  give  suitable  conditions  for 
the  development  of  the  bacillus  which  produces 
tetanus  or  lockjaw.  The  deaths  of  children 
from  lockjaw  following  a  Fourth  of  July  cele- 
bration have  often  exceeded  the  total  deaths 
in  a  Central  American  revolution.  The  tetanus 
bacillus  is  a  widely  distributed  organism,  whose 
normal  habitat  is  in  the  soil  and  which  is  usually 
present  on  the  dirty  hands  of  little  boys.  The 
toy-pistol  wounds  are  made  by  small  bits  of  paper 
or  metal  being  driven  into  the  skin  by  the  explo- 
sion of  the  cap.  The  wound  is  of  little  moment, 
the  surface  becomes  closed,  and  a  bit  of  foreign 
substance,  a  few  dead  cells  and  the  tetanus 
bacilli  from  the  surface  remain  enclosed  and  in 
a  few  days  the  fatal  disease  develops. 

Infection  of  the  surfaces  of  old  wounds  such 
as  the  surface  of  an  ulcer  takes  place  with  dif- 
ficulty. Large  numbers  of  leucocytes  which 
give  protection  by  phagocytosis  are  constantly 
passing  to  the  surface,  and  there  is  also  a  constant 
stream  of  fluid  towards  the  surface.  On  such 
a  surface  there  may  be  an  abundant  growth  of 
pathogenic  organisms,  but  no  infection  results. 

In  most  infections  there  is  a  focus  where  the 
infectious  organisms  are  localized;  this  may 
correspond  to  the  point  of  entrance  on  a  surface 


DISEASE  AND  ITS  CAUSES        143 

or  it  may  be  in  the  interior  of  the  body,  the 
organisms  being  deposited  there  after  entrance. 
At  this  primary  localization,  the  atrium  of  in- 
fection,^ the  organisms  multiply  and  from  this 
point  further  invasion  takes  place.  Many  second- 
ary foci  may  be  formed  in  the  organs  by  distri- 
bution of  the  organisms,  or  there  may  be  infection 
of  the  blood  and  fluids  of  the  body.  The  injuries 
which  are  produced  depend  upon  the  nature  of 
the  infecting  organisms.  The  most  common 
lesion  consists  in  the  death  of  the  tissue  about 
the  infecting  organisms.  In  most  cases  the  sum 
of  the  changes  are  so  characteristic  that  from 
them  the  nature  of  the  infection  is  easily  deter- 
mined, and  these  changes  often  give  names  to 
the  disease;  thus  tuberculosis  is  a  disease  charac- 
terized by  the  formation  of  tubercles  or  little 
nodules  in  the  body.  The  situation  of  the  foci 
of  disease  is  determined  by  many  conditions, 
the  most  important  being  the  varying  resistance 
of  the  different  organs  of  the  body  to  the  growth 
of  bacteria.  Certain  organs,  such  as  the  central 
nervous  system,  the  muscles,  the  testicles  and 
the  ovaries,  have  a  high  resistance  to  the  growth  of 
bacteria.  The  disease  may  be  localized  in  certain 
organs  because  only  in  these  do  the  bacteria  find 
favorable  conditions  for  growth.  In  spite  of  a 
high  general  resistance  to  infection  the  lesions  in 

1  The  comparison  here  is  with  the  atrium  of  a  Pompeiian 
house. 


144        DISEASE  AND   ITS  CAUSES 

chronic  glanders  are  most  marked  in  the  muscles, 
those  of  poliomyelitis  in  the  spinal  cord.  There 
are  few  bacterial  diseases  which  are  localized  in 
the  blood,  but  many  of  the  diseases  caused  by 
protozoa  have  this  localization.  In  every  infec- 
tion some  organisms  enter  the  blood,  which  acts 
as  a  carrier  and  deposits  them  in  the  organs. 

Bacteria  cause  disease  by  producing  substances 
called  toxines  which  are  poisonous  to  the  cells, 
and  of  which  two  sorts  are  distinguished.  One 
form  of  toxines  is  produced  by  the  bacteria  as  a 
sort  of  secretion,  and  is  formed  both  in  the  body 
and  when  the  bacteria  are  growing  in  cultures. 
Substances  of  this  character,  many  of  them 
highly  poisonous,  are  produced  both  by  animals 
and  plants.  They  may  serve  the  purpose  both 
of  offence  and  defence,  as  in  the  case  of  the  snake 
venom,  and  in  other  cases  they  seem  to  benefit 
their  producers  in  no  way  whatever,  and  may 
even  be  injurious  to  them.  After  the  different 
cereals  have  been  grown  for  succeeding  years  in 
the  same  place,  growth  finally  diminishes  not 
from  the  exhaustion  of  the  soil,  but  from  the 
accumulatiom  in  it  of  substances  produced  by 
the  plants.  Beneath  certain  trees,  as  the  Norway 
maple,  grass  will  not  grow,  and  it  has  been  shown 
that  the  tree  produces  substances  which  inhibit 
the  growth  of  grass.  When  bacteria  are  grown  in 
a  culture  flask,  growth  ceases  long  before  the 
nutritive  material  has  been  consumed,  from  the 


DISEASE  AND   ITS   CAUSES        145 

accumulation  of  waste  products  in  the  jfluid. 
The  other  class  of  toxic  substances,  called  endo- 
toxines,  are  not  secretion  products,  but  are  con- 
tained in  the  bacterial  substance  and  become 
active  by  the  destruction  and  disintegration  of 
the  bacteria.  They  can  be  artificially  produced 
by  grinding  up  masses  of  bacteria,  and  in  the 
body  the  destruction  and  solution  of  bacteria 
which  is  constantly  taking  place  sets  them  free. 
The  toxines  and  the  endotoxines  are  of  an  albu- 
minous nature,  and  act  only  when  they  come  in 
contact  with  the  living  cells  within  the  body. 
When  taken  into  the  alimentary  canal  they  are 
either  not  absorbed  or  so  changed  by  the  digestive 
fluids  as  to  be  innocuous.  Many  of  the  ordinary 
food  substances,  even  a  material  apparently  so 
simple  as  the  white  of  an  egg,  are  highly  in- 
jurious if  they  reach  the  tissues  in  an  unchanged 
form. 

By  means  of  these  substances  the  bacteria 
produce  such  changes  in  their  environment 
within  the  body  that  this  becomes  adapted  to 
their  parasitic  existence.  In  symbiosis  the  bac- 
teria probably  undergo  changes  by  which  they 
become  adapted  to  the  environment,  and  in 
parasitism  the  environment  becomes  adapted  to 
them.  In  the  same  way  man  can  change  his 
immediate  environment  by  means  of  clothing, 
artificial  heating,  etc.,  and  adapt  it  to  his  needs; 
or  by  hardening  his  body  he  can  adapt  it  to  the 


146        DISEASE  AND   ITS  CAUSES 

environment.  The  pathogenic  bacterium  finds 
the  living  tissue  hostile,  its  cells  devour  him,  the 
tissue  fluids  destroy  him,  and  by  means  of  the 
toxines  he  changes  the  environment  from  that 
of  living  to  dead  tissue,  or  in  other  ways  so  alters  it 
that  it  is  no  longer  hostile.  The  parasite  has  also 
means  of  passive  defence  comparable  to  the  armor 
of  the  warrior  in  the  past.  It  may  form  a  protective 
mantle  called  a  capsule  around  itself,  which  serves 
to  protect  it  from  the  action  of  the  body  fluids. 
Such  capsule  formation  is  a  very  common  thing  in 
the  pathogenic  organisms,  and  they  are  found  only 
when  these  are  growing  in  the  body  and  do  not 
appear  in  cultures  (Fig.  17 — c). 

It  is  evident  that  just  as  the  parasite  has  his 
weapons  of  offence  and  defence  so  has  the  host, 
otherwise  there  would  be  no  recovery  from  in- 
fectious diseases.  Although  many  of  the  infec- 
tious diseases  have  a  high  mortality,  which  in 
rare  instances  reaches  one  hundred  per  cent,  the 
majority  do  recover.  In  certain  cases  the  recov- 
ery is  attended  by  immunity,  the  individual 
being  protected  to  a  greater  or  less  degree  from 
a  recurrence  of  the  same  disease.  The  immunity 
is  never  absolute;  it  may  last  for  a  number  of 
years  only,  and  usually,  if  the  disease  be  again 
acquired,  the  second  attack  is  milder  than  the 
primary.  Probably  the  most  enduring  immunity 
is  in  smallpox,  although  cases  are  known  of  two 
and  even  three  attacks;    the  immunity  is  high 


DISEASE  AND   ITS   CAUSES        147 

in  scarlet  fever,  measles,  mumps  and  typhoid 
fever.  The  immunity  from  diphtheria  is  short, 
and  in  pneumonia,  although  there  must  be  a 
temporary  immunity,  future  susceptibility  to 
the  disease  is  probably  increased.  In  certain 
cases  the  immunity  is  only  local;  the  focus  of 
disease  heals  because  the  tissue  there  h9,s  evolved 
means  of  protection  from  the  parasite,  but  if 
any  other  part  of  the  body  be  infected,  the 
disease  pursues  the  usual  course.  A  boil,  for 
example,  is  frequently  followed  by  the  appear- 
ance of  similar  boils  in  the  vicinity  due  to  the 
infection  of  the  skin  by  the  micrococci  from  the 
first  boil,  which  by  dressings,  etc.,  have  become 
spread  over  the  surface. 

The  natural  methods  of  defence  of  the  host 
against  the  parasites  have  formed  the  main 
subject  in  the  study  of  the  infectious  diseases 
for  the  last  twenty  years.  Speculation  in  this 
territory  has  been  rife  and  most  of  it  fruitless, 
but  by  patient  study  of  disease  in  man  and  by 
animal  experimentation  there  has  been  gradually 
evolved  a  sum  of  knowledge  which  has  been  ap- 
plied in  many  cases  to  the  treatment  of  infectious 
diseases  with  immense  benefit.  Research  was 
naturally  turned  to  this  subject,  for  it  was  evident 
that  the  processes  by  which  the  protection  of 
the  body  was  brought  about  must  be  known 
before  there  could  be  a  really  rational  method 
of  treatment  directed  towards  the  artificial  in- 


148        DISEASE  AND   ITS  CAUSES 

duction  of  such  processes,  or  hastening  and 
strengthening  those  which  were  taking  place. 
Previous  to  knowledge  of  the  bacteria,  their 
mode  of  life,  their  methods  of  infection  and 
knowledge  of  the  defences  of  the  body,  most  of 
the  methods  of  prevention  and  treatment  of  the 
infectious  diseases  was  based  largely  on  con- 
jecture, the  one  brilliant  exception  being  the 
discovery  of  vaccination  by  Jenner  in  1798. 

The  host  possesses  the  passive  defences  of 
the  surfaces  which  have  already  been  considered. 
The  first  theories  advanced  in  explanation  of 
immunity  were  influenced  by  what  was  known 
of  fermentation.  One,  the  exhaustion  theory, 
assumed  that  in  the  course  of  disease  substances 
contained  in  the  body  and  necessary  for  the 
growth  of  the  bacteria  became  exhausted  and 
the  bacteria  died  in  consequence.  Another,  the 
theory  of  addition,  assumed  that  in  the  course 
of  the  disease  substances  inimical  to  the  bacteria 
were  formed.  Both  these  theories  were  inade- 
quate and  not  in  accord  with  what  was  known 
of  the  physiology  of  the  body.  The  most  general 
mode  of  defence  is  by  phagocytosis,  the  property 
which  many  cells  have  of  devouring  and  digest- 
ing solid  substances  (Fig.  16  —  p).  Although  this 
had  been  known  to  take  place  in  the  amoebae 
and  other  unicellular  organisms,  the  wide  extent 
of  the  process  and  its  importance  in  immunity 
was   first   recognized   by  Metschnikoff   in    1884 


DISEASE  AND   ITS  CAUSES        149 

and  the  phagocytic  theory  of  immunity  advanced 
and  defended  by  a  brilliant  series  of  experi- 
ments by  Metschnikoff  and  his  pupils  conducted 
in  the  Pasteur  Institute.  Metschnikoff's  first 
observations  were  made  on  the  daphnea,  a  small 
animalcule  just  visible  to  the  naked  eye  which 
lives  in  fresh  water.  The  structure  of  the  organ- 
ism is  simple,  consisting  of  an  external  and  in- 
ternal surface  between  which  there  is  a  space, 
the  body  cavity;  daphnese  are  transparent  and 
can  be  studied  under  the  microscope  while  living. 
Metschnikoff  observed  that  certain  of  them  in 
the  aquarium  gradually  lost  their  transparency 
and  died,  and  examining  these  he  found  they 
were  attacked  by  a  species  of  fungus  having  long, 
thin  spores.  These  spores  were  taken  into  the 
intestine  with  other  food;  they  penetrated  the  thin 
wall  of  the  intestine,  passed  into  the  body  cavity, 
multiplied  there,  and  in  consequence  the  animal 
died.  In  many  cases,  however,  those  penetrating 
became  enclosed  in  cells  which  the  body  cavity 
contains  and  which  correspond  with  the  leuco- 
cytes of  the  blood;  in  these  the  spores  were 
digested  and  destroyed.  The  daphnese  in  which 
this  took  place  recovered  from  the  infection. 
Here  was  a  case  in  which  all  the  stages  of 
an  infectious  disease  could  be  directly  fol- 
lowed under  the  microscope,  and  the  whole 
process  was  simple  in  comparison  with  infec- 
tions  in  the  higher   animals.     The    pathogenic 


150       DISEASE  AND  ITS  CAUSES 

organism  was  known,  the  manner  and  site  of 
invasion  was  clear,  it  was  also  evident  that  if 
the  multiplication  of  the  parasite  was  un- 
checked the  animal  died,  but  if  the  parasite 
was  opposed  by  the  body  cells  and  destroyed 
the  animal  recovered.  The  studies  were  carried 
further  into  the  diseases  of  the  higher  animals,  and 
it  was  found  the  leucocytes  in  these  played  the 
same  part  as  did  the  cells  in  the  body  cavity  of 
the  daphnea.  The  introduction  of  bacteria  into 
certain  animals  was  followed  by  their  destruc- 
tion within  cells  and  no  disease  resulted;  if  this 
did  not  take  place,  the  bacteria  multiplied  and 
produced  disease.  Support  also  was  given  the 
theory  by  the  demonstration  at  about  the  same 
time  that  in  most  of  the  infectious  diseases  the 
leucocytes  of  the  blood  became  increased  in 
number, — that  in  pneumonia,  for  instance,  in- 
stead of  the  usual  number  of  eight  thousand  in  a 
cubic  millimeter  of  blood,  there  were  often  thirty 
thousand  or  even  fifty  thousand.  At  about  the 
same  time  also  chemotaxis,  or  the  action  of  chemi- 
cal substances  in  attracting  or  repelling  organ- 
isms, excited  attention,  and  all  these  facts  together 
became  woven  into  the  theory.  It  was  soon 
seen,  however,  that  this  theory,  based  as  it  was 
on  observation  and  supported  by  the  facts  ob- 
served, was  not,  at  least  in  its  first  crude  form, 
capable  of  general  application.  Many  animals 
have  natural  immunity  to  certain  diseases;    they 


DISEASE   AND   ITS  CAUSES        151 

do  not  have  the  disease  under  natural  conditions, 
nor  do  they  acquire  the  disease  when  the  organ- 
isms causing  it  are  artificially  introduced  into 
their  tissues  by  inoculation.  Such  natural  im- 
munity seemed  to  be  unconnected  with  defence  by 
phagocytosis,  for  the  leucocytes  of  the  animal 
might  or  might  not  have  phagocytic  reaction 
to  the  particular  organisms  to  which  the  animal 
was  immune.  It  was  also  seen  that  recovery 
from  infection  in  certain  diseases  was  uncon- 
nected with  phagocytosis.  It  had  also  been 
demonstrated,  by  German  observers  chiefly, 
that  the  serum  of  the  blood,  the  colorless  fluid 
in  which  the  corpuscles  float,  was  itself  destruc- 
tive, and  that  in  an  animal  rendered  immune  to 
a  special  bacterium  the  destructive  action  of 
the  serum  on  that  organism  was  greatly  increased. 
In  this  hostile  serum  the  bacteria  often  became 
clumped  together  in  masses,  the  bodies  became 
swollen,  broken  up,  and  finally  disintegrated. 
This  property  of  the  serum  was  described  as 
due  to  a  substance  in  the  serum  called  alexine, 
which  in  the  immune  animal  became  greatly 
increased  in  amount.  It  was  even  denied  by 
some  that  phagocytosis  of  living  bacteria  took 
place,  and  that  all  those  included  in  the  cells  were 
dead,  having  been  destroyed  in  the  first  instance 
by  the  serum.  The  strife  became  a  national 
one  between  the  French  and  Germans,  —  on  the 
one  side  in  France  the  phagocytic  theory  was 


152        DISEASE  AND   ITS  CAUSES 

defended,  and  in  Germany,  on  the  other,  the 
theory  of  serum  immunity.  The  mass  of  ex- 
perimental work  which  poured  from  the  labora- 
tories of  the  two  countries  in  attack  and  defence 
became  so  great  that  it  could  not  easily  be  fol- 
lowed. It  had  a  good  influence  because,  without 
the  stimulation  of  this  national  rivalry,  the  knowl- 
edge which  gradually  arose  from  this  work  would 
not  have  been  so  quickly  acquired.  It  is  inter- 
esting that  the  mode  of  action  of  the  serum  in 
destroying  bacteria  was  demonstrated  not  by 
a  German  but  by  Bordet,  a  French  observer 
and  a  pupil  of  Metschnikoff.  He  showed  that 
the  serum  contained  two  distinct  substances, 
each  necessary  for  the  destructive  action.  The 
separate  action  of  these  substances  can  be  studied 
since  one  is  thermolabile,  or  destroyed  by  heating 
the  serum  to  one  hundred  and  thirty-three  de- 
grees; the  other  thermostabile,  or  capable  of 
withstanding  a  greater  degree  of  heat.  These 
substances  are  known  only  by  their  efiFect,  they 
have  never  been  separated  from  the  serum.  The 
thermostabile  substance,  or  amboceptor,  as  it 
is  generally  called,  has  in  itself  no  destructive 
action  on  the  bacteria;  but  in  some  way  so  alters 
them  that  they  can  be  acted  on  by  the  thermo- 
labile substance  called  complement  whose  action 
is  destructive.  The  amount  of  amboceptor  may 
increase  in  the  course  of  infection  and  its  for- 
mation stimulated,  the  amount  of  complement 


DISEASE  AND   ITS  CAUSES        153 

remains  unchanged.  The  action  of  the  ambo- 
ceptor is  specific,  that  is,  directed  against  a  single 
species  of  bacterium  only;  the  destructive  power 
of  the  blood  may  be  very  great  against  a  single 
bacterium  species  and  have  no  effect  on  others. 
There  seem  naturally  to  be  many  different 
amboceptors  in  the  blood,  and  the  number  may 
be  very  greatly  increased.  It  has  been  shown 
as  a  result  of  the  work  of  many  investigators 
that  the  shield  has  two  faces, — there  is  destruction 
both  by  cells  and  fluids  and  there  is  interaction 
by  both.  The  amboceptors  so  necessary  for  the 
destructive  action  of  the  serum  are  produced 
by  the  body  cells,  particularly  the  leucocytes. 
The  serum  assists  in  pagocytosis  by  the  action 
on  bacteria  of  substances  called  opsonins  which 
are  contained  in  it,  and  the  formation  of  which 
can  be  very  greatly  stimulated.  Again,  not  all 
inclusion  of  bacteria  within  leucocytes  is  indica- 
tive of  phagocytosis;  in  many  cases  the  bacteria 
seem  to  find  the  best  conditions  for  existence 
within  the  leucocytes,  and  these  and  not  the 
bacteria  are  destroyed. 

So  far  it  has  been  shown  that  the  best  defence 
of  the  body  is,  as  is  the  best  defence  in  war, 
by  offensive  measures,  as  illustrated  by  phago- 
cytosis and  destruction  by  the  serum.  Both 
of  these  actions  can  be  increased  by  their  ex- 
ercise just  as  the  strength  of  muscular  con- 
traction can  be  increased  by  exercise,  and  the 


154        DISEASE  AND   ITS  CAUSES 

facility  for  doing  everything  increased  by  habit. 
Certain  of  the  infectious  diseases  are,  as  has  been 
said,  essentially  toxic  in  their  nature,  and  in 
cultures  the  organisms  produce  poisonous  sub- 
stances. By  the  injection  into  the  tissues  of 
such  substances  the  same  disturbances  are  pro- 
duced as  when  the  bacteria  are  injected.  Such 
a  disease  is  diphtheria.  In  this  there  is  only  a 
superficial  invasion  of  the  tissues.  The  diph- 
theria bacilli  are  located  on  the  surface  of  the 
tonsils  or  pharynx  or  windpipe,  where,  as  a  result 
of  their  action,  the  membrane  so  characteristic 
of  the  disease  is  produced.  The  membrane  may 
be  the  cause  of  death  when  it  is  so  extensively 
formed  as  to  occlude  the  air  passages,  but  the 
prominent  symptoms  of  the  disease,  the  fever, 
the  weakness  of  the  heart  and  the  great  prostra- 
tion are  due  not  to  the  presence  of  the  membrane, 
but  to  the  action  of  toxic  substances  which  are 
formed  by  the  bacteria  growing  in  the  super- 
ficial lesions  and  absorbed.  Tetanus,  or  lock- 
jaw, is  another  example  of  these  essentially  toxic 
diseases.  The  body  must  find  some  means  of 
counteracting  or  destroying  these  injurious  toxic 
substances.  It  does  this  by  forming  antagonis- 
tic substances  called  antitoxines,  which  act  not 
by  destroying  the  toxines,  but  by  uniting  with 
them,  the  compound  substance  being  harmless. 
It  has  been  found  that  the  production  of  anti- 
toxine  can  be  so  stimulated  by  the  injection  of 


DISEASE  AND   ITS   CAUSES        155 

toxine  that  the  blood  of  the  animal  used  for  the 
purpose  contains  large  amounts  of  antitoxine. 
The  horse  is  used  in  this  way  to  manufacture 
antitoxine,  and  the  serum  injected  into  a  patient 
with  diphtheria  has  a  curative  action,  a  greater 


WSw^m 


Fig.  18.  —  Diagram  to  illustrate  Ehrlich's  theory  op 
ANTITOXINE  FORMATION.  The  surface  of  the  cell  (n)  is  cov- 
ered with  receptors  some  of  which  (6)  fit  the  toxine  molecule, 
(a)  allowing  the  toxine  to  act  upon  the  cell.  Under  the  stimu- 
lus of  this  the  cell  produces  these  receptors  in  excess  which 
enter  into  the  blood  and  there  combine  with  the  toxine  as  in 
a»  6»,  thus  anchoring  it  and  preventing  it  from  acting  upon  the 
cells.    The  receptors  c  and  d  do  not  fit  the  toxine  molecule. 

amount  being  thus  introduced  than  the  patient 
can  manufacture. 

A  very  ingenious  theory  which  well  accords 
with  the  facts  has  been  given  by  Ehrlich  in  ex- 
planation of  the  production  of  antitoxine  and 
of  the  reaction  between  toxine  and  antitoxine 
(Fig.  18).    This  is  based  on  the  hypothesis,  which 


156        DISEASE  AND   ITS  CAUSES 

is  in  accord  with  all  facts  and  generally  accepted, 
that  the  molecules  which  enter  into  the  structure 
of  any  chemical  substance  have  in  each  particular 
substance  a  definite  arrangement,  and  that  in 
a  compound  substance  each  elementary  sub- 
stance entering  into  the  compound  molecule  has 
chemical  affinities,  most  of  which  may  be  satis- 
fied by  finding  a  suitable  mate.  Ehrlich  assumes 
that  the  very  complex  chemical  substances  which 
form  the '  living  cells  have  many  unsatisfied 
chemical  affinities,  and  that  it  is  due  to  this  that 
molecules  of  substances  adapted  for  food  can 
enter  the  cells  and  unite  with  them;  but  there 
must  be  some  coincidence  of  molecular  structure 
to  enable  the  union  to  take  place,  the  comparison 
being  made  of  the  fitting  of  a  key  into  a  lock. 
The  toxines  —  that  produced  by  the  diphtheria 
bacillus  being  the  best  example  —  are  substances 
whose  molecular  structure  enables  them  to  com- 
bine with  the  cells  of  the  body,  the  combination 
being  effected  through  certain  chemical  affinities 
belonging  to  the  cells  termed  receptors.  Unless 
the  living  cells  have  receptors  which  will  enable 
the  combination  with  the  toxine  to  take  place, 
no  effect  can  be  produced  by  the  toxine  and  the 
cells  are  not  injured.  This  is  the  case  in  an 
animal  naturally  immune  to  the  action  of  the 
diphtheria  bacillus  or  its  toxines.  In  the  case 
of  the  susceptible  animal  the  receptors  of  the 
cells  of  the  diflFerent  organs  combine  with  the 


DISEASE  AND   ITS  CAUSES        157 

toxine  to  a  greater  or  less  extent,  which  explains 
the  fact  that  different  degrees  of  injury  are 
produced  in  the  different  tissues;  the  toxine  of 
tetanus,  or  lockjaw,  for  example,  combines  by 
preference  with  the  nervous  tissue,  that  of  diph- 
theria with  the  lymphatic  tissue.  It  is  known 
that  in  accordance  with  the  general  law  of  in- 
jury and  repair,  a  loss  in  any  part  of  the  body 
stimulates  the  tissue  of  the  same  kind  to  new 
growth  and  the  loss  is  thus  repaired;  it  is  as- 
sumed that  the  cell  receptors  which  combine 
with  the  toxine  are  lost  for  the  cell  which  then 
produces  them  in  excess.  The  receptors  so 
produced  pass  into  the  blood,  where  they  com- 
bine with  the  toxine  which  has  been  absorbed; 
the  combination  is  a  stable  one,  and  the  toxine 
is  thus  prevented  from  combining  with  the  tissue 
cells.  The  anti toxine  which  is  formed  during  the 
disease,  and  the  production  of  which  in  the  horse 
can  be  enormously  stimulated  by  the  injection 
of  toxine,  represents  merely  the  excess  of  cell 
receptors,  and  when  the  serum  of  the  horse 
containing  them  is  injected  in  a  case  of  diph- 
theria the  same  combination  takes  place  as  in 
the  case  of  receptors  provided  by  the  patient. 
In  the  case  of  the  destruction  of  bacteria  in 
the  blood  by  the  action  of  amboceptor  and 
complement,  the  amboceptor  must  be  able  to 
combine  with  both  the  bacterial  cell  and  the 
complement  which  brings  about  its  destruction. 


158        DISEASE  AND   ITS  CAUSES 

and  just  as  antitoxine  is  formed  so  new  ambo- 
ceptors may  be  formed. 

Few  hypotheses  have  been  advanced  in  science 
which  are  more  ingenious,  in  better  accord  with 
the  facts,  have  had  greater  importance  in  en- 
abling the  student  to  grasp  the  intricacies  of 
an  obscure  problem,  and  which  have  had  an 
equal  influence  in  stimulating  research.  The 
immunity  which  results  from  disease  in  accord- 
ance with  this  theory,  is  due  not  to  conditions 
preventing  the  entrance  of  organisms  into  the 
body,  but  to  greater  aptitude  on  the  part  of  the 
cells  to  produce  these  protective  substances  hav- 
ing once  learned  to  do  so.  An  individual  need 
not  practise  for  many  years,  having  once  learned 
them,  those  combinations  of  muscular  action  used 
in  swimming;  but  the  habit  at  once  returns 
when  he  falls  into  the  water. 

Infectious  diseases  and  recovery  are  phases 
of  the  struggle  for  existence  between  parasite 
and  host,  and  illustrate  the  power  of  adaptation 
to  environment  which  is  so  striking  a  character- 
istic of  living  matter. 


CHAPTER  VIII 

Secondary,  Terminal  and  Mixed  Infections.  —  The 
Extension  of  Infection  in  the  Individual.  —  Tuber- 
CTTLosis.  —  The  Tubercle  Bacillus.  —  Frequency  op 
THE  Disease.  —  The  Primary  Foci.  —  The  Extension 
OF  Bacilli.  —  The  Discharge  of  Bacilli  from  the 
Body.  —  Influence  of  the  Seat  of  Disease  on  the 
Discharge  of  Bacilli.  —  The  Intestinal  Diseases.  — 
Modes  of  Infection.  —  Infection  by  Sputum  Spray. 
—  Infection  of  Water  Supplies.  —  Extension  of  In- 
fection BY  Insects.  —  Trypanosome  Diseases.  —  Sleep- 
ing Sickness.  —  Malaria.  —  The  Part  played  by  Mos- 
quitoes.—  Parasitism  in  the  Mosquito. — Infection 
as  influenced  by  Habits  and  Customs.  —  Hookworm 
Disease. — Inter-relation  between  Hum.\n  and  Animal 
Diseases.  —  Plague.  —  Part  played  by  Rats  in  Trans- 
mission. —  The  Present  Epidemic  of  Plague. 

The  infectious  diseases  are  often  complicated 
by  secondary  infections,  some  other  organism 
finding  opportunity  for  invasion  in  the  presence 
of  the  injuries  produced  in  the  primary  disease. 
In  many  diseases,  such  as  diphtheria,  scariet  fever 
and  smallpox,  death  is  frequently  due  to  the 
secondary  infection.  The  secondary  invaders 
not  only  find  local  conditions  favoring  a  suc- 
cessful attack,  but  the  activity  of  the  tissue 
cells  on  which  the  production  of  protective  sub- 
stances essentially  depends  has  suffered  by  the 
primary  infection,  or  the  cells  are  occupied  in 
meeting  the  exigencies  of  this.  The  body  is  in 
the   position  of  a  state   invaded   by  a   second 

1,)9 


160        DISEASE  AND   ITS  CAUSES 

power  where  all  its  forces  and  resources  are  en- 
gaged in  repelling  the  first  attack. 

What  are  known  as  terminal  infections  occur 
shortly  before  death.  No  matter  what  the 
disease  which  causes  death,  in  the  last  hours  of 
life  the  body  usually  becomes  invaded  by  organ- 
isms which  find  their  opportunity  in  the  then 
defenceless  tissues,  and  the  end  is  often  hastened 
by  this  invasion. 

There  are  also  mixed  infections  in  which  two 
different  organisms  miite  in  attack,  each  in  some 
way  assisting  in  the  action  of  the  other.  The 
best  known  example  of  this  is  in  the  highly  in- 
fectious disease  of  swine  known  as  hog  cholera. 
It  has  been  showTi  that  in  this  disease  two  organ- 
isms are  associated,  —  one  an  invisible  and  filtera- 
ble organism,  and  the  other  a  bacillus.  It  was  first 
supposed  that  the  bacillus  was  the  specific  organ- 
ism ;  it  was  found  in  the  lesions  and  certain,  but 
not  all,  the  features  of  the  disease  were  produced 
by  inoculating  hogs  with  pure  cultures.  The 
disease  so  produced  is  not  contagious,  and  the 
contagious  element  seems  to  be  due  to  the  filter- 
able virus. 

The  modes  of  transmission  of  infectious  diseases 
are  of  great  importance  and  are  the  foundation 
of  measures  of  public  health.  In  the  preceding 
chapter  we  have  seen  that  in  the  infected  indi- 
vidual the  disease  extends  from  one  part  of  the 
body  to  another.     There  is  a  primary  focus  of 


DISEASE  AND   ITS  CAUSES        161 

disease  from  which  the  extension  takes  place, 
and  the  study  of  the  modes  of  extension  in  the 
individual  throws  some  light  on  the  much  more 
difficult  subject  of  the  transmission  of  disease 
from  one  individual  to  another.  There  are  four 
ways  by  which  extension  in  the  individual  may 
take  place. 

1.  By  continuity  of  tissue,  an  adjoining  tissue 
or  organ  becoming  infected  by  the  extension 
of  a  focus  of  infection. 

2.  By  means  of  lymphatics.  Organisms  easily 
enter  these  vessels  which  are  in  continuity  with 
the  tissue  spaces  and  receive  the  exudate  from 
the  focus  of  infection.  The  organisms  are 
carried  to  the  lymph  nodes,  which,  acting  as 
filters,  retain  them  and  for  a  time  prevent  a 
further  extension.  The  following  illustrates  the 
importance  of  the  part  the  nodes  may  play  in 
mechanically  holding  back  a  flood  of  infection. 
A  physician  examined  after  death  the  body  of 
a  person  who  died  from  infection  with  a  very 
virulent  micrococcus  and  in  the  course  of  the 
examination  slightly  scratched  a  finger.  One 
of  the  organs  of  the  body  was  removed,  sent  to 
a  laboratory  and  received  by  a  laboratory  worker, 
a  woman  physician,  who  had  slight  abrasions 
and  fissures  in  the  skin  of  the  hands  from  contact 
with  irritating  chemicals.  In  the  course  of  a 
few  hours  the  wound  on  the  finger  of  the  man 
became    inflamed,    intensely    painful,    and    red 


162        DISEASE  AND   ITS  CAUSES 

lines  extended  up  the  arm  in  the  course  of  the 
lymphatic  vessels,  showing  that  the  organisms 
were  in  the  lymphatics  and  causing  inflammation 
in  their  course.  The  lymph  nodes  in  the  arm- 
pit into  which  these  vessels  empty  became  greatly 
inflamed,  swollen,  and  an  abscess  formed  in  them 
which  was  opened.  There  was  high  fever,  great 
prostration,  a  serious  illness  from  which  the  man 
did  not  recover  for  several  months.  The  woman 
only  handled  the  organ  which  was  sent  to  the 
laboratory  in  order  to  place  it  in  a  fluid  for 
preservation.  She  also  had  a  focus  of  infection 
of  a  finger  with  the  same  red  lines  on  the  arm, 
showing  extension  by  the  lymphatics;  but  there 
was  no  halt  of  the  infection  in  the  armpit,  for 
all  the  lymph  nodes  there  had  been  removed 
several  years  before  in  the  course  of  an  opera- 
tion for  a  tumor  of  the  breast.  A  general  in- 
fection of  the  blood  took  place,  there  was  very 
high  fever,  and  death  followed  in  a  few  days. 
The  halt  of  the  infection  is  important  in  allow- 
ing time  for  the  hody  to  make  ready  its  means 
of  defence.  One  cannot  avoid  comparing  the 
lymph  node  with  a  strong  fortress  thrown  in 
the  path  of  a  victorious  invading  army  behind 
which  the  defenders  may  gather  and  which 
affords  them  time  to  renovate  their  strength. 

3.  By  means  of  the  blood.  The  blood  vessels 
are  universally  distributed,  the  smaller  vessels 
have  thin  waUs  easily  ruptured  and  easily  pene- 


DISEASE  AND   ITS   CAUSES        163 

trated.  It  is  probable  that  in  every  infection 
some  organisms  enter  the  blood  which,  under 
usual  conditions,  is  peculiarly  hostile  to  bacteria. 
These  may,  however,  be  carried  by  the  blood  to 
other  organs  and  start  foci  of  infection  in  these. 

4.  By  means  of  continuous  surfaces.  The 
bacteria  may  either  grow  along  such  surfaces 
forming  a  continuous  or  more  or  less  broken 
layer,  or  may  be  carried  from  place  to  place  in 
the  fluids  which  bathe  them. 

All  these  modes  of  extension  are  well  shown 
in  tuberculosis.  This  disease  is  caused  by  a 
small  bacillus  which  does  not  produce  spores,  has 
no  power  of  saphrophytic  growth  under  natural 
conditions,  and  is  easily  destroyed.  Moisture 
and  darkness  are  favorable  conditions  for  its 
existence,  sunlight  and  dryness  the  reverse. 
There  are  three  varieties  or  strains  of  the  tubercle 
bacilli  which  infect  respectively  man,  cattle 
and  birds,  and  each  class  of  animals  shows  con- 
siderable resistance  to  the  varieties  of  the  bacil- 
lus which  are  most  infectious  for  the  others. 

The  primary  seat  of  the  infection  in  man  is 
generally  in  the  upper  part  of  the  lung.  The 
organisms  settle  on  the  surface  here  and  cause 
multiplication  of  the  cells  and  an  inflammatory 
exudate  in  a  small  area.  With  the  continuous 
growth  of  the  bacilli  in  the  focus,  adjoining  areas 
of  the  lung  become  aflFected,  and  there  is  further 
extension  in  the  immediate  vicinity  by  means 


164        DISEASE  AND   ITS  CAUSES 

of  the  lymphatics.  Small  nodules  are  formed 
and  larger  areas  by  their  coalescence.  Infection 
with  tuberculosis  is  so  common  that  at  least 
three-fourths  of  all  individuals  over  forty  show 
evidences  of  it.  The  examination  of  two  hun- 
dred and  twenty -five  children  of  the  average  age 
of  five  years  who  had  died  of  diphtheria  show  ed 
tuberculous  infection  in  one-fifth  of  the  cases  and 
the  frequency  of  infection  increases  with  age. 
The  defence  on  the  part  of  the  body  is  chiefly 
by  the  formation  of  dense  masses  of  cicatricial 
tissue  which  walls  off  the  affected  area  and  in 
which  the  bacilli  do  not  find  favorable  condi- 
tions for  growth.  This  mode  of  defence,  which 
is  probably  combined  wdth  the  production  of 
substances  antagonistic  to  the  toxines  produced 
by  the  bacilli,  is  so  efficacious  that  in  the  great 
majority  of  cases  no  further  extension  of  the 
process  takes  place.  In  certain  cases,  however, 
the  growth  of  the  bacilli  in  the  focus  is  un- 
checked, the  tissue  about  them  is  killed  and 
becomes  converted  into  a  soft  semi-fluid  mate- 
rial; further  extension  then  takes  place.  All 
parts  of  the  enormous  surface  of  the  lungs  are 
connected  by  means  of  the  system  of  air  tubes 
or  bronchi,  and  the  bacilli  have  favorable  oppor- 
tunity for  distribution,  which  is  facilitated  by 
sudden  movements  of  the  air  currents  in  the 
lung  produced  by  coughing.  The  defence  of 
the  body  can  still  keep  pace  with  the  attack. 


DISEASE  AND   ITS   CAUSES        165 

and  even  in  an  advanced  stage  the  infection  can 
be  checked  in  some  cases  permanently;  in  others 
the  check  is  but  temporary,  the  process  of  soften- 
ing continues,  and  large  cavities  are  produced 
by  the  destruction  of  the  tissue.  On  the  inner 
surface  of  these  cavities  there  may  be  a  rapid 
growth  of  bacilli. 

From  the  lungs  the  bacilli  are  carried  by  the 
lymphatics  to  the  lymph  nodes  at  the  root  of 
the  lungs,  in  which  a  similar  process  takes  place; 
this,  on  the  whole,  is  favorable,  because  further 
extension  by  this  route  is  for  a  time  blocked. 
The  extension  by  means  of  surfaces  continues, 
the  abundant  sputum  which  is  formed  in  the 
lungs  and  which  contains  large  numbers  of 
bacilli,  becomes  the  vehicle  of  transportation. 
The  windpipe  and  larynx  may  become  infected, 
the  back  parts  of  each  are  more  closely  in  con- 
tact with  the  sputum  and  are  the  parts  most 
generally  infected.  A  large  part  of  the  sputum 
is  swallowed  and  infection  of  the  intestine  takes 
place,  the  lesions  taking  the  form  of  large  ulcers. 
From  the  intestinal  ulcers  there  is  further  ex- 
tension by  means  of  the  lymphatics,  to  the 
large  lymph  nodes  In  the  back  of  the  abdominal 
cavity  (Fig.  8  —  25) ;  the  bacilli  may  also  pass 
from  the  ulcers  into  the  abdominal  cavity  and 
be  distributed  over  the  surface  of  the  peritoneum 
resulting  in  tuberculous  peritonitis.  When  the 
disease  has  reached  an  advanced  stage,  bacilli 


166        DISEASE  AND   ITS  CAUSES 

in  small  numbers  continually  pass  into  the  blood 
and  are  distributed  by  this  over  the  body,  pro- 
ducing small  nodules  in  many  places.  In  rare 
cases  distribution  by  the  blood  is  the  principal 
method  of  extension,  and  immense  numbers  of 
small  foci  of  disease  are  produced,  the  form  of 
disease  being  known  as  acute  miliary  tuber- 
culosis. Although  the  bacilli  are  distributed 
everywhere,  certain  organs,  as  the  brain  and 
muscles,  are  usually  exempt,  because  in  these 
the  conditions  are  not  favorable  to  further 
growth  of  the  bacilli.  Tuberculosis,  although 
frequently  a  very  acute  disease,  is  usually  one 
of  the  best  types  of  a  chronic  disease  and  may 
last  for  many  years.  The  chronic  form  is  char- 
acterized by  periods  of  slow  or  rapid  advance 
when  conditions  arise  in  the  body  favorable  for 
the  growth  of  the  bacilli,  and  periods  when  the 
disease  is  checked  and  quiescent,  the  defensive 
forces  of  the  body  having  gained  the  upper 
hand.  Often  the  intervention  of  some  other 
disease  so  weakens  the  defences  of  the  body 
that  the  bacilli  again  find  their  opportunity. 
Thus  typhoid  fever,  scarlet  fever  and  other  dis- 
eases may  be  followed  by  a  rapidly  fatal  ad- 
vance of  the  tuberculosis,  starting  from  some 
old   and  quiescent  focus  of  the  disease. 

Tuberculosis  is  also  one  of  the  best  examples 
of  what  is  known  as  latent  infection.  In  this 
the   infectious   organisms   enter   the   body   and 


DISEASE  AND  ITS  CAUSES        167 

produce  primary  lesions  in  which  the  organisms 
persist  but  do  not  extend  owing  to  their  being 
enclosed  in  a  dense  and  resistant  tissue,  or  to 
the  production  of  a  local  immunity  to  their  action. 
Dr.  Head  has  recently  examined  the  children 
of  households  in  which  there  was  open  tuber- 
culosis in  some  member  of  the  household.  By 
open  tuberculosis  is  understood  a  case  from  which 
bacilli  are  being  discharged.  He  found  with 
scarcely  an  exception  that  all  the  children  in 
such  families  showed  evidences  of  infection. 
The  detection  of  slight  degrees  of  tuberculous 
infection  is  now  made  easy  by  certain  skin  re- 
actions on  inoculation  of  the  skin  with  a  substance 
derived  from  the  tubercle  bacilli.  Such  latent 
infections  may  never  become  active  and  in  the 
majority  of  cases  do  not.  When,  however,  in 
consequence  of  some  intercurrent  disease  or 
conditions  of  malnutrition  the  general  defences 
of  the  body  become  weakened  extension  follows. 
Such  latent  infections  explain  the  enormous 
frequency  of  tuberculosis  in  prisons.  Under  the 
general  prison  conditions  infection  in  the  prisons 
probably  does  not  take  place  to  any  extent,  and 
the  disease  is  as  common  when  the  prisoners  are 
kept  in  individual  cells  as  in  common  prisons. 
It  is  probable  that  in  these  cases  the  prisoners 
have  latent  tuberculosis  when  entering,  and  the 
disease  becomes  active  under  the  moral  and 
physical  depression  which  prison  life  entails. 


168       DISEASE  AND  ITS   CAUSES 

For  the  extension  of  infection  from  one  indi- 
vidual to  another  the  infecting  organisms  must 
in  some  way  be  transferred.  The  most  important 
of  the  conditions  influencing  this  are  the  locahza- 
tion  of  the  disease  and  the  character  of  the  in- 
fectious organisms,  particularly  with  regard  to 
their  resistance  to  the  conditions  met  with  out- 
side of  the  body.  The  seat  of  disease  influences 
the  discharge  of  organisms;  thus,  if  the  disease 
involve  any  of  the  surfaces  the  organisms  become 
mingled  with  the  secretions  of  the  surface  and 
are  discharged  with  these.  If  the  seat  of  disease 
be  in  the  lungs,  the  throat  or  the  mouth,  the 
sputum  forms  the  medium  of  extension,  which 
can  take  place  in  many  ways.  The  sputum 
may  become  dried,  forms  part  of  the  dust  and  the 
organisms  enter  with  the  inspired  air.  The 
organisms  which  cause  most  of  the  diseases 
in  which  the  sputum  becomes  infectious  are 
quickly  destroyed  by  conditions  in  the  open,  such 
as  the  sunlight  and  drying;  street  dust  does  not 
play  so  prominent  a  part  in  extension  as  is  gen- 
erally supposed.  Organisms  find  much  more 
favorable  conditions  within  houses.  It  is  now  gen- 
erally recognized  that  infection  with  tuberculosis 
does  not  take  place  in  the  open,  but  in  houses 
in  which  the  bacilli  on  being  discharged  are  not 
destroyed.  The  hands,  the  clothing  and  surround- 
ings even  with  the  exercise  of  the  greatest  care 
may  become  soiled  with  the  saliva. 


DISEASE   AND   ITS  CAUSES        169 

It  has  been  shown  that  in  coughing  and  speak- 
ing very  fine  particles  of  spray  are  formed  by  the 
intermingUng  of  air  and  saliva,  which  may  be 
projected  a  considerable  distance  and  remain  float- 
ing in  the  air  for  some  time.  These  particles  are 
so  fine  as  to  be  invisible;  they  may  be  inspired, 
and  their  presence  in  the  air  forms  an  area  of  in- 
determinate extent  around  the  infected  person 
within  which  such  infection  is  possible.  Such 
spray  formation  is  also  an  important  means  of  the 
extension  of  infection  in  the  sick  individual,  for  it 
is  continually  formed  and  inspired.  It  is  in  this 
way  that  the  extreme  prevalence  of  broncho-pneu- 
monia in  infants  and  young  children  is  to  be 
explained.  No  matter  what  the  essential  disease, 
an  almost  constant  finding  in  young  children 
after  death  is  small  areas  of  inflammation  in 
the  lungs  in  and  around  the  terminations  of  the 
air  tubes.  The  situation  renders  it  evident  that 
the  organisms  which  caused  the  lesions  entered 
the  lung  by  the  air  tubes.  The  mouth  of  the 
child  is  unclean  and  harbors  numbers  of  the 
same  sort  of  organisms  as  those  causing  the  lung 
inflammation;  but  in  the  absence  of  such  a 
mode  of  infection  as  is  given  by  spray  formation 
it  is  difficult  to  see  how  the  extension  from  the 
mouth  to  the  lungs  could  take  place.  The  weak- 
ened condition  of  the  body  in  these  cases  favors 
the  secondary  infection. 

If   the   disease   be  located   in   the  intestines, 


170        DISEASE  AND   ITS  CAUSES 

as  in  typhoid  fever  and  dysentery,  the  organisms 
are  contained  in  the  fecal  discharges,  and  by 
means  of  these  the  infection  is  extended.  In 
typhoid  fever,  dysentery  and  cholera  massive  in- 
fections of  the  populace  may  take  place  from  the 
contamination  of  a  water  supply  and  the  disease 
be  extended  over  an  entire  city.  One  of  the  most 
striking  instances  of  this  mode  of  extension  was  in 
the  epidemic  of  cholera  in  Hamburg  in  1892. 
There  were  two  sources  of  water  supply,  one  of 
which  was  infected,  and  the  cases  were  distributed 
in  the  city  in  the  track  of  the  infected  supply. 
Many  such  instances  have  been  seen  in  typhoid 
fever.  Certain  articles  of  food,  particularly  milk, 
serve  as  sources  of  infection.  This  is  more  apt  to 
happen  when  the  organism  causing  the  infection 
grows  easily  outside  of  the  body.  A  few  such  or- 
ganisms entering  into  the  milk  can  multiply  enor- 
mously in  a  few  hours  and  increase  the  amount  of 
infectious  material.  In  all  these  cases  the  sick  in- 
dividual remains  a  source'  of  infection,  for  it  is 
almost  impossible  to  avoid  some  contamination  of 
the  body  and  the  immediate  surroundings  with 
the  organisms  contained  in  the  discharges. 

Transmission  by  air  plays  but  little  part  in 
the  extension  of  infection.  In  such  a  disease  as 
smallpox,  where  the  localization  is  on  the  surface 
of  the  body,  the  organisms  are  contained  in  or 
on  the  thin  epithelial  scales  which  are  constantly 
given   off.     These   are  light,  and   may   remain 


DISEASE  AND   ITS  CAUSES        171 

floating  in  the  air  and  carried  by  air  currents 
just  as  is  the  pollen  of  plants.  There  seem  to 
have  been  cases  of  smallpox  where  other  modes 
of  more  direct  transmission  could  be  excluded^ 
and  in  which  the  organisms  were  carried  in  the 
air  over  a  considerable  space.  All  sorts  of  in- 
termediate objects,  both  livang  and  inanimate, 
such  as  persons,  domestic  animals,  toys,  books, 
money,  etc.,  can  serve  as  conveyors  of  infection. 

Insects  play  a  most  important  part  in  the 
transmission  of  disease,  and  in  certain  cases, 
as  when  a  disease  is  localized  in  the  blood,  this 
is  the  only  means  of  transmission.  There  are 
three  ways  in  which  the  insect  plays  the  role  of 
conveyor. 

1.  The  insect  may  play  a  purely  passive  part 
in  that  its  exterior  surface  becomes  contaminated 
with  the  discharges  of  the  sick  person,  and  in  this 
way  the  organisms  of  disease  may  be  conveyed 
to  articles  of  food,  etc.  The  ordinary  house  fly 
conveys  in  this  way  the  organisms  of  typhoid  and 
dysentery.  Flies  seek  the  discharges  not  only  for 
food,  but  for  the  purpose  of  depositing  their  eggs, 
and  the  hairy  and  irregular  surface  of  their  feet 
facilitates  contamination  and  conveyance.  When 
flies  eat  such  discharges  the  organisms  may  pass 
through  the  alimentarj'^  canal  unchanged  and  be 
deposited  with  their  feces;  they  also  often  vomit 
or  regurgitate  food,  and  in  this  way  also  con- 
taminate objects.    Flies  very  greedily  devour  the 


172        DISEASE  AND   ITS   CAUSES 

sputum  of  tuberculous  patients,  and  the  tubercle 
bacilli  contained  in  this  pass  through  them  un- 
changed and  are  deposited  in  their  feces. 

2.  Diseases  which  are  localized  in  the  blood 
are  transmitted  by  biting  flies.  The  biting 
apparatus  becomes  contaminated  with  the  or- 


FiG.  19.  —  Trtpanosomes  from  birds.  All  the  trj^jano- 
somes  are  very  much  alike.  They  contain  a  nucleus  repre- 
sented by  the  dark  area  in  the  centre  and  a  fur-like  membrane 
terminating  in  a  long  whip-like  flagellum.  They  have  the 
power  of  very  active  motion  within  the  blood. 

ganisms  contained  in  the  blood,  and  these  are 
directly  inoculated  into  the  blood  of  the  next 
victim.  The  trypanosome  diseases  form  the 
best  example  of  this  mode  of  transmission.  The 
trypanosomes  are  widely  distributed,  exclusively 
parasitic,  flagellated  protozoa  which  hve  in  the 
blood  of  a  large  number  of  animals  and  birds 
(Fig.  19).    They  may  give  rise  to  fatal  diseases, 


DISEASE  AND   ITS  CAUSES        173 

but  in  most  cases  there  is  mutual  adaptation 
of  host  and  parasite  and  they  seem  to  do  no 
harm.  One  of  the  most  dangerous  diseases  in 
man,  the  African  sleeping  sickness,  is  caused 
by  a  trypanosome,  and  the  disease  of  domestic 
cattle  in  Africa,  nagana,  or  tsetse  fly  disease, 
is  also  so  produced.  In  certain  regions  of 
Africa  where  a  biting  fly,  the  Glossina  mor- 
sitans,  occurs  in  large  numbers,  it  has  long 
been  known  that  cattle  bitten  by  these  flies 
sickened  and  died,  and  this  prevented  the  set- 
tling and  use  of  the  land.  In  the  blood  of 
the  sick  cattle  swarms  of  trypanosomes  are 
found.  The  source  from  which  the  tsetse  fly 
obtained  the  trypanosomes  which  it  conveyed 
to  the  cattle  was  unknown  until  it  was  dis- 
covered that  similar  trypanosomes  exist  in  the 
blood  of  the  wild  animals  which  inhabit  the 
region,  but  these  have  acquired  by  long  resi- 
dence in  the  region  immunity  or  adaptation 
to  the  parasite  and  no  disease  is  produced. 
With  the  gradual  extension  of  settlement  of  the 
country  and  the  accompanying  destruction  of 
wild  life  the  disease  is  diminishing.  Some  of  the 
inter-relations  of  infections  are  interesting.  The 
destruction  of  wild  animals  in  South  Africa  which, 
by  removing  the  sources  of  nagana,  rendered  the 
settlement  of  the  country  possible  was  due  chiefly 
to  the  introduction  of  another  infectious  disease, 
rinderpest,  which  not  only  destroyed  the  wild 


174        DISEASE  AND   ITS  CAUSES 

animals  but  produced  great  destruction  of  the 
domestic  cattle  as  well. 

The  sleeping  sickness  has  many  features  of 
interest.  In  the  old  slavery  days  it  was  found 
that  the  negroes  from  the  Congo  region  in  the 
course  of  the  voyage  or  after  they  were  landed 
sometimes  were  affected  with  a  peculiar  disease. 
They  were  lethargic,  took  little  notice  of  their 
surroundings,  slept  easily  and  finally  passed 
into  a  condition  of  somnolence  in  which  they 
took  no  food  and  gradually  died.  There  was  no 
extension  of  the  disease  and  it  was  attributed 
to  extreme  homesickness  and  depression.  A 
similar  disease  has  been  known  for  more  than 
one  hundred  years  on  the  west  coast  of  Africa, 
and  attracted  a  good  deal  of  interest  and  curi- 
osity on  account  of  the  peculiar  lethargy  which  it 
produced  and  from  which  it  has  received  the  name 
of  "sleeping  sickness."  Although  apparently  in- 
fectious in  its  native  haunts,  it  lost  the  power  of 
spreading  from  man  upon  removal  to  regions 
where  it  did  not  prevail.  At  first  confined  to 
a  very  small  region  on  the  Niger  river,  it  gradu- 
ally extended  with  the  development  of  trade 
routes  and  the  general  increase  of  communi- 
cations which  trade  brings,  until  it  prevails 
in  the  entire  Congo  basin,  in  the  British  and 
German  possessions  in  East  Africa,  and  is  ex- 
tending north  and  south  of  these  regions.  The 
cause  of  the  disease  and  its  mode  of  conveyance 


DISEASE  AND  ITS  CAUSES        175 

was  discovered  in  1903.  The  fly  Glossina  pal- 
palis  which  conveys  the  disease  is  a  biting  fly 
about  the^ize  of  the  common  house  fly  and  lives 
chiefly  in  the  vicinity  of  water.  When  such  a  fly 
bites  an  individual  who  has  sleeping  sickness  its  bite 
can  convey  the  disease  to  monkeys,  on  whom  the 
transmission  experiments  were  made.  After  bit- 
ing the  fly  is  infectious  for  a  period  of  two  days. 
After  this  it  is  harmless,  unless  it  again  obtains  a 
supply  of  living  trypanosomes.  There  is  quite  a 
period  in  which  there  are  no  symptoms  of  the  dis- 
ease, although  trypanosomes  are  found  in  the  blood 
and  in  the  lymph  nodes,  and  the  individual  is  a 
source  of  infection.  The  peculiar  lethargy  which 
has  given  the  disease  its  name  does  not  appear  un- 
til the  nervous  system  is  invaded  by  the  parasites. 
It  is  impossible  to  compute  accurately  the  num- 
bers of  deaths  from  this  disease  —  in  the  region 
of  Victoria  Nyanza  alone  the  estimates  extend  to 
hundreds  of  thousands. 

3.  In  the  third  mode  of  insect  conveyance 
the  insect  does  not  play  a  merely  passive  role, 
but  becomes  a  part  of  the  disease,  itself  under- 
going infection,  and  a  period  in  the  life  cycle  of 
the  organism  takes  place  within  it.  In  all  these 
cases  quite  a  period  of  time  must  elapse  before 
the  insect  is  capable  of  transmitting  the  disease; 
in  malaria,  which  is  the  best  type  of  such  a  disease, 
this  period  is  ten  days.  Malaria  is  due  to  a  small 
protozoan,  the  Plasmodium  malarice,  which  was 


176        DISEASE  AND   ITS  CAUSES 

discovered  by  Lavaran,  a  French  investigator, 
in  1882.  The  organism  lives  within  or  on  the 
surface  of  the  red  blood  corpuscles.  It  first 
appears  as  a  very  minute  colorless  body  with 
active  amoeboid  movements,  and  increases  in 
size,  attacks  a  succession  of  corpuscles,  and  finally 
attains  a  size  as  large  as  or  larger  than  a  cor- 
puscle. The  corpuscles  attacked  become  pale 
by  the  destruction  of  haemoglobin,  swell  up  and 
disintegrate,  the  haemoglobin  becoming  converted 
into  granules  of  black  pigment  inside  the  para- 
site. Having  attained  a  definite  size  the  organism 
forms  a  rosette  and  divides  into  a  number  of 
forms  similar  to  the  smallest  seen  inside  the 
corpuscles;  these  small  forms  enter  other  cor- 
puscles and  the  cycle  again  begins.  This  cycle 
of  development  takes  place  in  forty -eight  hours, 
and  segmentation  is  always  accompanied  by  a 
paroxysm  of  the  disease  shown  in  a  chill  followed 
by  fever  and  sweating  which  is  due  to  the  effect 
of  substances  liberated  by  the  organism  at  the 
time  of  segmentation.  A  patient  may  have  two 
crops  of  the  parasite  developing  independently 
in  the  blood,  and  the  two  periods  of  segmentation 
give  a  paroxysm  for  each,  so  that  the  paroxysms 
may  appear  at  intervals  of  twenty-four  hours 
instead  of  forty-eight  (Fig.  20).  This  cycle  of 
development  may  continue  for  an  indefinite  time, 
and  there  may  be  such  a  rapid  increase  in  the 
parasites  as  to   bring  about   the  death  of   the 


DISEASE  AND   ITS  CAUSES        177 

individual;  but  with  him  the  parasite  would  also 
perish,  for  there  would  be  no  way  of  extending 
the  infection  and  providing  a  new  crop.  The 
disease  has  been  transmitted  by  injecting  the 
infected  blood  into  a  normal  individual. 


Fig.  20.  —  P.\rt  of  the  cycle  of  development  of  the 
ORGANISM  of  m.\lari.\.  a-g.  Cycle  of  forty-eight  hour  develop- 
ment, the  period  of  chill  coinciding  with  the  appearance  of 
/  and  g  in  the  blood.  The  organisms  g,  which  result  from 
segmentation,  attack  other  corpuscles  and  a  new  cycle  begins. 
h.  The  male  form  or  microgametocyte,  with  the  protruding 
and  actively  moving  spermatozoa,  one  of  which  is  shown 
free,  i  and  j  are  the  macrogametes  or  female  forms,  k  shows 
one  of  these  in  the  act  of  being  fertilized  by  the  entering  sper- 
matozoon. The  differentiation  into  male  and  female  forms 
takes  place  in  the  blood,  the  further  development  of  the 
sexual  cycle  within  the  mosquito. 

If  a  mosquito  of  the  species  anopheles  bites  the 
affected  person,  it  obtains  a  large  amount  of 
blood  which  contains  many  parasites.  Within 
the  mosquito  the  parasite  undergoes  a  further 
development  into  male  and  female  sexual  forms, 
which  may  also  form  in  the  blood,  termed  respec- 
tively microgametocyte  and   macrogamete.    From 


178        DISEASE  AND   ITS  CAUSES 

the  microgametocyte  small  flagellate  bodies, 
the  male  sexual  elements  microgametes  or  sper- 
matozoa, develop  and  fertilize  the  macrogametes; 
after  fertilization  this  develops  into  a  large  body, 
the  oocyst  which  is  attached  to  the  wall  of  the 
stomach  of  the  mosquito.  Within  the  oocyst, 
innumerable  small  bodies,  the  sporozoites,  develop, 
make  their  way  into  the  salivary  glands  and  are 
injected  into  the  individual  who  becomes  the  prey 
of  the  mosquito,  and  again  the  cycle  of  develop- 
ment begins.  The  presence  of  the  parasite  within 
the  mosquito  does  not  constitute  a  disease.  So  far 
as  can  be  determined,  life  goes  on  in  the  usual 
way,  and  its  duration  in  the  insect  is  not 
shortened. 

The  nature  of  the  parasite  which  produces 
yellow  fever  is  unknown,  for  it  belongs  to  the 
filterable  viruses;  the  infectious  material,  how- 
ever, has  been  shown  by  inoculation  to  exist  in 
the  blood,  and  the  disease  is  transmitted  by  a 
mosquito  of  another  species,  the  stegomyia. 
The  development  cycle  within  this  takes  a  period 
of  twelve  days,  which  time  must  elapse  after  the 
mosquito  has  bitten  before  it  can  transmit  the 
disease.  Here  again  the  mutual  interdependence 
of  knowledge  is  shown.  Nothing  could  have 
seemed  less  useful  than  the  study  of  mosquitoes, 
the  differentiation  of  the  different  species,  their 
mode  of  life,  etc.,  and  yet  without  this  knowledge 
discoveries  so  beneficial  and  of  such  far-reaching 


DISEASE   AND   ITS   CAUSES        179 

importance  to  the  whole  human  race  as  that 
of  the  cause  and  mode  of  transmission  of  malaria 
and  yellow  fever  would  have  been  impossible; 
for  it  could  easily  have  been  shown  that  the 
ordinary  culex  mosquito  played  no  role.  The 
role  which  insects  may  play  in  the  transmission 
of  disease  was  first  shown  by  Theobald  Smith 
in  this  country,  in  the  transmission  by  a  tick 
of  the  disease  of  cattle  known  as  Texas  fever. 
The  infecting  organism  pyrosoma  bigenimum  is 
a  tiny  pear-shaped  parasite  of  the  red  corpuscles. 
Smith's  investigations  on  the  disease,  pubhshed  in 
1893,  is  one  of  the  classics  in  medicine,  and  one 
of  the  few  examples  of  an  investigation  which  has 
not  been  changed  or  added  to  by  further  work. 
One  of  the  most  interesting  methods  of  ex- 
tension of  infection,  showing  on  what  small 
circumstances  infection  may  depend,  is  seen  in 
the  case  of  the  hookworm  disease,  which  causes 
such  devastation  in  the  Southern  States.  The 
organism  which  produces  the  disease,  the  Uncin- 
aria,  belongs  to  the  more  highly  developed  para- 
sites, and  is  a  small  round  worm  one-third  of  an 
inch  long.  The  worms  which  inhabit  the  intes- 
tines have  a  sharp  biting  mouth  by  which  they 
fasten  themselves  to  the  mucous  membrane  and 
devour  the  blood.  The  most  prominent  symp- 
tom of  the  disease  is  anaemia,  or  loss  of  blood, 
due  not  only  to  the  direct  eating  of  the  para- 
site,  but  to   bleeding   from   the   small  wounds 


180        DISEASE  AND   ITS  CAUSES 

caused  by  its  bite.  Large  numbers  of  eggs  are 
produced  by  the  parasite  which  are  passed  out 
with  the  feces,  which  becomes  the  only  infectious 
material.  In  a  city  provided  with  water-closets 
and  a  system  of  sewerage  there  would  be  no 
means  of  extension  of  infection.  The  eggs  in 
the  feces  in  conditions  of  warmth  and  moisture 
develop  into  small  crawling  larvae  which  can 
penetrate  the  skin,  producing  inflammation  of 
this,  known  in  the  region  as  the  ground  itch. 
The  larvae  enter  the  circulation  and  are  carried 
to  the  lungs,  where  they  perforate  the  capillaries 
and  reach  the  inner  surface;  from  this  they  pass 
along  the  windpipe,  and  then  by  way  of  the 
gullet  and  stomach  reach  their  habitat,  the  small 
intestine.  Unfortunately,  the  habits  and  poverty 
of  the  people  in  every  way  facilitate  the  exten- 
sion of  the  infection.  There  is  no  proper  disposal 
of  the  feces,  few  of  the  houses  have  even  a  privy 
attached  to  them,  and  the  feces  are  distributed 
in  the  vicinity  of  the  houses.  This  leads  to  con- 
tamination of  the  soil  over  wide  areas.  Most 
of  the  inhabitants  of  the  country  go  barefoot 
the  greater  part  of  the  year,  and  this  gives  ready 
means  of  contact  with  the  larvae  which  crawl  over 
the  surface  of  the  ground.  The  disease  is  neces- 
sarily associated  with  poverty  and  ignorance,  the 
amount  of  blood  is  reduced  to  a  low  point,  and 
industry,  energy  and  ambition  fall  with  the 
blood  reduction;    the  schools  are  few  and  in- 


DISEASE  AND   ITS  CAUSES        181 

efficient;  the  children  are  backward,  for  no 
child  can  learn  whose  brain  cells  receive  but  a 
small  proportion  of  the  necessary  oxygen;  and 
a  general  condition  of  apathy  and  hopelessness 
prevails  in  the  effected  communities.  The  con- 
trol of  the  disease  depends  upon  the  disinfection 
of  the  feces,  or  at  least  their  disposal  in  some 
hygienic  method,  the  wearing  of  shoes,  and  the 
better  education  of  the  people,  all  of  which  con- 
ditions seem  almost  hopeless  of  attainment.  The 
infection  is  also  extended  by  means  of  the  negroes 
who  harbor  the  parasite,  but  who  have  acquired  a 
high  degree  of  immunity  to  its  effects  and  whose 
hygienic  habits  are  even  worse  than  those  of  the 
whites.  The  organism  was  probably  imported 
with  the  negroes  from  Africa  and  is  one  of  the 
legacies  of  slavery. 

The  diseases  of  animals  are  in  many  ways 
closely  linked  with  those  of  man.  In  the  case 
of  the  larger  parasites,  such  as  the  tapeworms 
and  the  trichina,  there  is  a  direct  interchange  of 
disease  with  animals,  certain  phases  of  the  life 
cycle  of  the  organisms  are  passed  in  man  and 
others  in  various  of  the  domestic  animals.  A 
small  inconspicuous  tapeworm  inliabits  the 
intestine  of  dogs  and  seems  to  produce  no 
ill  effects.  The  eggs  are  passed  from  the  dog, 
taken  into  man,  and  result  in  the  formation 
of  large  cystic  tumors  which  not  infrequently 
cause   death.      Where    the    companionship    be- 


182        DISEASE  AND   ITS  CAUSES 

tween  dog  and  man  is  very  close,  as  in  Iceland, 
the  cases  are  numerous. 

Most  of  the  diseases  in  animals  caused  by 
bacteria  and  protozoa  are  not  transmitted  to 
man,  but  there  is  a  conspicuous  exception. 
Plague  is  now  recognized  as  essentially  an  animal 
disease  aflFecting  rats  and  other  small  rodents, 
and  from  these  the  disease  from  time  to  time 
makes  excursions  to  the  human  family  with  dire 
results.  The  greatest  epidemics  of  which  we 
have  any  knowledge  are  of  plague.  In  the  time 
of  Justinian,  542  b.  c,  a  great  epidemic  of  plague 
extended  over  what  was  then  regarded  as  the 
inhabited  earth.  This  pandemic  lasted  for  fifty 
years,  the  disease  disappeared  and  appeared 
again  in  many  places  and  caused  frightful  de- 
struction of  life.  Cities  were  depopulated,  the 
land  in  many  places  reverted  to  a  wilderness, 
and  the  works  of  man  disappeared.  The  actual 
mortality  cannot  be  known,  but  has  been  esti- 
mated at  fifty  milUons.  Plague  played  a  large 
part  in  the  epidemics  of  the  Middle  Ages.  An 
epidemic  started  in  1346  and  had  as  great  an 
extension  as  the  Justinian  plague,  destroying 
a  fourth  of  the  inhabitants  of  the  places  attacked ; 
and  during  the  fifteenth  and  sixteenth  and  seven- 
teenth centuries  the  disease  repeatedly  raised 
its  head,  producing  smaller  and  greater  epidemics, 
the  best  known  of  which,  from  the  wonderful 
description  of  De  Foe,  is  that  of  London  in  1665, 


DISEASE  AND   ITS   CAUSES        183 

and  called  the  Black  Death.  Little  was  heard 
of  the  disease  in  the  nineteenth  century,  although 
its  existence  in  Asia  was  known.  In  1894  it 
appeared  in  Hong  Kong,  extended  to  Canton, 
thence  to  India,  Japan,  San  Francisco,  Mexico, 
and,  in  fact,  few  parts  of  the  tropics  or  temperate 
regions  of  the  earth  have  been  free  from  it.  Mor- 
tality has  varied  greatly,  being  greatest  in  China 
and  in  India;  in  the  last  the  estimate  since  1900 
is  seven  million  five  hundred  thousand  deaths. 
The  disease  is  caused  by  a  small  bacillus  dis- 
covered in  1894  which  forms  no  spores  and  is 
easily  destroyed  by  sunlight,  but  in  the  dark  is 
capable  of  living  with  undiminished  virulence 
for  an  indefinite  time.  The  disease  in  man 
appears  in  two  forms,  the  most  common  known 
as  bubonic  plague,  from  the  great  enlargement 
of  the  lymph  nodes,  those  of  the  groin  being 
most  frequently  affected.  The  more  fatal  form 
is  known  as  pneumonic  plague,  and  in  this  the 
lungs  are  the  seat  of  the  disease. 

In  the  old  descriptions  of  the  disease  it  was 
frequently  mentioned  that  large  numbers  of  dead 
rats  were  found  when  it  was  prevalent,  and  the 
most  striking  fact  of  the  recent  investigations  is 
the  demonstration  that  the  infection  in  man  is  due 
to  transference  of  the  bacillus  from  infected  rats. 
There  are  endemic  foci  of  the  disease  where  it 
exists  in  animals,  the  present  epidemic  having 
started  from  such  a  focus  in  Northern  China,  in 


184        DISEASE  AND   ITS  CAUSES 

which  region  the  Tarabagan,  a  small  fur-bearing 
animal  of  the  squirrel  species,  was  infected.  Rats 
are  easily  infected,  the  close  social  habits  of  the 
animal,  the  vermin  which  they  harbor,  and  the 
habits  of  devouring  their  dead  fellows  favor  the 
extension  of  infection.  The  disease  extends 
from  the  rat  to  man  chiefly  by  means  of 
the  fleas  which  contain  the  bacilli,  and  in  cases  of 
pneumonic  plague  from  man  to  man  by  means 
of  sputum  infection.  The  disease  once  estab- 
lished in  animals  tends  to  remain,  the  virus  being 
kept  alive  by  transmission  from  animal  to 
animal,  and  the  persistence  of  the  infection  is 
favored  by  mild  and  chronic  cases. 


CHAPTER  IX 

Disease  Carriers.  —  The  Relation  between  Sporadic 
Cases  of  Infectious  Disease  and  Epidemics.  —  Small- 
pox. —  Cerebro-Spinal    Meningitis.  —  Polyomyelitis. 

—  Variation  in  the  Susceptibility  of  Individuals.  — • 
Conditions  which  may  influence  Susceptibility.  — 
Racial  susceptibility.  —  Influence  of  Age  and  Sex. 

—  Occupation  and  Environment.  —  The  Age  Period 
of  Infectious  Diseases. 

We  have  seen  that  insects  serve  as  carriers 
of  disease  in  two  ways :  in  one,  by  becoming 
contaminated  with  organisms  they  serve  as 
passive  carriers,  and  in  the  other  they  undergo  in- 
fection and  form  a  Hnk  in  the  disease.  The  more 
recent  investigations  of  modes  of  transmission 
of  infectious  diseases  have  shown  that  man,  in 
addition  to  serving  while  sick  as  a  source  of 
infection,  may  serve  as  a  passive  carrier  in  two 
ways.  For  infection  to  take  place  not  only 
must  the  pathogenic  organism  be  present,  but  it 
must  be  able  to  overcome  the  passive  and  active 
defences  of  the  body  and  produce  injury.  Patho- 
genic organisms  may  find  conditions  favorable 
for  growth  on  the  surfaces  of  the  body,  and  may 
live  there,  but  be  unable  to  produce  infection, 
and  the  individual  who  simply  harbors  the 
185 


186        DISEASE  AND   ITS   CAUSES 

organisms  can  transmit  them  to  others.  Such 
an  individual  may  be  a  greater  source  of  infection 
than  one  with  the  disease,  because  there  is  no 
suspicion  of  danger.  The  organisms  which  thus 
grow  on  the  surfaces  have  in  some  cases  been 
shown  to  be  of  diminished  virulence,  but  in 
others  have  full  pathogenic  power.  Such  pas- 
sive carriers  of  infection  have  been  found  for 
a  number  of  diseases,  as  cerebro-spinal  menin- 
gitis, diphtheria,  poliomyelitis  and  cholera.  In 
all  these  cases  the  organisms  are  most  frequently 
found  in  those  individuals  who  have  been  exposed 
to  infection  as  members  of  a  family  in  which 
there  have  been  cases  of  disease.  The  other 
sort  of  carrier  has  had  and  overcome  the  disease, 
but  mutual  relations  have  been  established  with 
the  organism  which  continues  to  live  in  the 
body  cavity.  Diphtheria  bacilli  usually  linger 
in  the  throat  after  convalescence  is  estabUshed, 
and  until  they  have  disappeared  the  individual 
is  more  dangerous  than  one  actually  sick  with 
the  disease.  Health  officers  have  recognized  this 
in  continuing  the  quarantine  against  the  disease 
until  the  organism  disappears.  In  typhoid  fever 
bacilli  may  remain  in  the  body  for  a  long  time 
and  be  continually  discharged,  as  in  the  well- 
known  case  of  "typhoid  Mary."  * 

*  This  was  the  case  of  a  woman,  by  occupation  a  cook, 
whose  numerous  exchanges  of  service  were  accompanied  by 
the  appearance  of  cases  of  typhoid  fever  in  the  families. 


DISEASE  AND   ITS  CAUSES        187 

Single  cases  of  certain  infectious  diseases  may 
appear  in  a  community  year  after  year,  and 
at  interv^s  the  cases  become  so  numerous  that 
the  disease  is  said  to  be  epidemic.  Such  a  disease 
is  smallpox.  This  is  a  highly  infectious  disease, 
towards  which  all  mankind  is  susceptible.  Com- 
plete protection  against  the  dise£lse  can  be  con- 
ferred by  Jenner's  discovery  of  vaccination. 
The  disease  becomes  modified  when  transferred 
to  cattle,  producing  what  is  known  as  cowpox, 
in  which  vesicles  similar  to  those  of  smallpox 
appear  on  the  skin.  The  inoculation  of  man 
with  the  contents  of  such  a  vesicle  produces  a 
mild  form  of  disease  known  as  vaccinia,  which 
protects  the  individual  from  smallpox.  This 
protection  is  fully  as  adequate  as  that  produced 
by  an  attack  of  smallpox,  and  we  are  war- 
ranted in  saying  that  if  thorough  vaccination, 
or  the  inoculation  with  vaccinia,  were  carried 
out  smallpox  would  disappear.  There  are  great 
diflSculties  in  the  way  of  carrying  out  effective 
vaccination  of  the  whole  population,  which 
are  accentuated  by  the  active  opposition  of 
people  who  are  ignorant  and  wilfully  remain  so. 
There  exists  in  every  state  a  number  of  people 
unprotected  by  vaccination,  and  among  these 
single  cases   of   smallpox   appear.     The   unpro- 

This  became  so  marked  that  an  examination  was  made  and 
she  was  found  to  be  a  typhoid  carrier  and  as  such  constantly 
discharging  typhoid  bacilli.     She  is  now  isolated. 


188        DISEASE  AND   ITS  CAUSES 

tected  individuals  gradually  increase  in  number, 
forming  an  inflammable  material  awaiting  the 
spark  or  infection  which  produces  a  conflagration 
in  the  one  case  and  an  epidemic  in  the  other. 

Cerebro-spinal  meningitis  is  another  example 
of  a  disease  which  exists  in  sporadic  and  epidemic 
form.  This  disease  is  caused  by  a  small  micro- 
coccus, the  organisms  joined  in  pairs.  The  seat 
of  the  disease  is  in  the  meninges  or  membranes 
around  the  brain  and  spinal  cord.  The  micro- 
cocci enter  the  body  from  the  throat  and  nose, 
and  either  pass  directly  from  here  into  the 
meninges,  or  they  enter  into  the  blood  and  are 
carried  by  this  into  the  meninges.  The  organisms 
are  easily  destroyed  and  cannot  long  survive  the 
conditions  outside  the  body,  so  that  for  infection 
to  take  place  the  transmission  must  be  very  direct. 
Carriers  who  have  the  organisms  in  the  throat, 
but  who  do  not  have  the  disease,  are  the  principal 
agents  in  dissemination.  The  mortality  is  high, 
and  even  in  recovery  permanent  damage  is  often 
done  to  the  brain  or  to  the  organs  of  special 
sense.  Sporadic  cases  constantly  occur  in  small 
numbers,  and  it  is  difficult  or  impossible  to  trace 
any  connection  between  these  cases.  At  varying 
intervals,  often  twenty  years  intervening,  an 
epidemic  appears  which  sometimes  remains 
local  in  a  city  or  state,  sometimes  extends  to 
adjoining  cities  or  states,  and  may  even  extend 
over  a  very  large  area.     In  the  epidemics  the 


DISEASE  AND   ITS   CAUSES        189 

mortality  is  much  higher  than  in  the  sporadic 
cases.  The  same  explanation  given  for  small- 
pox cannot  apply  here,  for  there  is  not  a  similar 
accumulation  of  susceptible  material.  We  know 
there  is  a  great  deal  of  variation  in  the  virulence 
of  the  different  pathogenic  organisms,  and  the 
virulence  can  be  artificially  increased  and  dimin- 
ished. In  epidemics  of  meningitis  the  virulence 
of  the  organisms  is  increased,  as  is  shown  by  the 
greater  mortality.  It  is  highly  probable  that 
such  epidemics  are  due  to  changes  which  arise 
in  the  organisms  from  causes  we  do  not  know  and 
which  increase  their  capacity  for  harm.  It  is 
possible  that  such  a  change  would  convert  a 
carrier  into  a  case  of  disease,  the  organism  ac- 
quiring greater  powers  of  invasion.  Such  a 
strain  of  organisms  arising  in  one  place  and 
producing  an  epidemic  could  be  transported 
to  another  locality  and  exert  the  same  action, 
or  similar  changes  in  the  organisms  could  arise 
simultaneously  in  a  number  of  places.  Analogies 
to  such  conditions  are  given  in  plants.  In  cer- 
tain plants  it  has  been  shown  that  from  unknown 
causes  there  appears  a  tendency  to  the  produc- 
tion of  variations.  A  very  beautiful  herbaceous 
peony  known  as  "  Bridesmaid "  after  having 
grown  for  a  number  of  years  in  single  form,  in 
one  year  wherever  grown  suddenly  became 
double.  The  peculiar  thing  with  the  lower 
unicellular  organisms  is  that  the  changes  which 


190        DISEASE  AND   ITS  CAUSES 

so  arise  do  not  tend  to  become  permanent,  the 
organism  reverts  to  its  usual  character,  the 
disease  to  its  sporadic  type. 

A  very  fatal  form  of  poliomyelitis  has  for  a 
number  of  years  prevailed  in  Sweden.  In  the 
United  States  there  have  been  continually  a 
number  of  single  cases  of  the  disease,  and  it  is 
not  impossible  that  a  more  pathogenic  strain  of 
the  organism  has  developed  in  Sweden  and  has 
been  imported  into  this  country,  giving  rise  to 
the  much  greater  extension  of  the  disease  in  a 
number  of  places. 

The  most  cursory  study  of  the  infectious 
diseases  shows  that  there  is  great  variation  in 
the  susceptibility  of  individuals.  Even  in  the 
most  severe  epidemics  all  are  not  equally  affected, 
some  escape  the  infection,  others  have  the  dis- 
ease lightly,  others  severely,  some  die.  Chance 
enters  into  this,  but  plays  a  small  part,  for  the 
same  varying  individual  susceptibility  is  shown 
experimentally.  If  a  given  number  of  animals 
of  the  same  species,  age  and  weight,  even  those 
from  the  same  litter,  be  inoculated  with  a  given 
number  of  bacteria  shown  to  be  pathogenic  for 
that  species,  the  results  differ.  If  the  dose  be 
necessarily  fatal,  death  will  take  place  at  inter- 
vals; if  a  dose  smaller  than  the  fatal  be  used, 
some  animals  will  die,  others  will  recover.  The 
defences  of  the  organism  being  centred  in  the 
activity  of  the  living  tissue,  any  condition  which 


DISEASE  AND   ITS  CAUSES        191 

depresses  cell  activity  may  have  an  effect  in 
increasing  susceptibility  to  infection.  Animals 
which  ordinarily  are  not  susceptible  to  infection 
with  a  certain  organism  may  be  made  so  by 
prolonged  hunger,  or  fatigue,  by  the  influence 
of  narcotics,  by  reduction  of  the  body  tempera- 
ture, by  loss  of  blood.  In  man  prolonged  fatigue, 
cold,  the  use  of  alcohol  to  excess  and  even  psychic 
depression  increases  susceptibility.  It  has  been 
shown  that  such  conditions  are  accompanied 
by  a  diminution  in  the  power  of  the  blood  to 
destroy  bacteria. 

There  is  variation  in  the  susceptibility  to 
infection  in  the  different  races  of  man.  If  a 
race  be  confined  to  one  habitat  with  close  inter- 
course between  the  people,  such  a  race  may 
acquire  a  high  degree  of  immunity  to  local  dis- 
eases by  a  gradual  weeding  out  of  the  individuals 
who  are  most  susceptible.  A  degree  of  compara- 
tive harmony  may  be  gradually  established 
between  host  and  parasite,  as  is  the  case  in  wild 
animals.  These  have  few  diseases,  the  weak 
die,  the  resistant  breed;  they  harbor,  it  is  true, 
large  numbers  of  parasites,  but  there  is  mutual 
adjustment  between  parasite  and  host.  Diseases 
in  animals  greatly  increase  under  the  artificial 
conditions  of  domestication.  Certain  highly 
specialized  breeds  of  cattle,  as  the  Alderneys, 
are  much  more  susceptible  to  tuberculosis  than 
the  less  specialized.     The  high  development  of 


192        DISEASE  AND   ITS  CAUSES 

the  variation  which  consists  in  a  marked  abihty 
to  produce  milk  fat  is  probably  combined  with 
other  qualities,  shown  in  diminished  resistance  to 
disease,  and  under  natural  conditions  the  varia- 
tion would  not  have  persisted.  The  introduction 
of  a  new  disease  into  an  isolated  people  has  often 
been  attended  with  dire  consequences.  It  is  much 
the  same  thing  with  the  introduction  of  disease 
of  plants.  In  Europe  the  brown-tail  moth  and 
the  gypsy  moth  produce  continuously  a  certain 
amount  of  damage  to  the  trees,  but  their  para- 
sitic enemies  have  developed  with  them  and 
check  their  increase.  These  pests  were  brought 
to  this  country  in  which  there  were  no  condi- 
tions retarding  their  increase  and  have  produced 
great  damage. 

It  is  very  diflficult  to  estimate  the  degree  of 
racial  susceptibility.  The  negro  race  seems  to 
be  more  susceptible  to  certain  diseases,  such  as 
tuberculosis  and  smallpox,  less  so  to  others,  as 
yellow  fever,  malaria  and  uncinariasis.  What 
are  apparently  differences  in  susceptibility  may 
be  explained  by  racial  customs.  A  statistical  in- 
quiry into  death  in  India  from  poisonous  snakes 
might  be  interpreted  as  showing  a  marked 
resistance  on  the  part  of  the  white  to  the  action 
of  the  venom,  but  it  is  merely  a  question  of  the 
boots  of  the  whites  and  the  naked  feet  and  legs 
of  the  natives.  The  relatively  greater  frequency 
of  smallpox  in  the  blacks  is  due  to  the  greater 


DISEASE  AND   ITS   CAUSES        193 

difficulties  in  carrying  out  vaccination  measures 
among  them  and  the  greater  opportunity  for 
infection  which  results  from  their  less  hygienic 
life.  It  has  always  been  noted  that  when  plague 
prevails  in  Oriental  cities,  the  natives  are  more 
frequently  attacked  than  are  Europeans.  This 
does  not  depend  upon  differences  in  suscepti- 
bility, but  on  the  better  hygienic  conditions  of 
the  whites  which  prevent  the  close  relation 
to  rats  and  vermin  by  which  infection  is  ex- 
tended. There  would  be  but  little  extension  of 
the  hookworm  disease  in  a  community  where 
shoes  were  worn  and  the  habits  were  cleanly. 

It  is  by  no  means  improbable  that  the  forma- 
tion of  the  habits  of  civilization  was  influenced  by 
infection.  Most  of  these  habits,  such  as  personal 
cleanliness,  the  avoidance  of  close  contact,  the 
demand  for  individual  utensils  for  eating  and 
drinking,  are  all  of  distinct  advantage  in  opposing 
infection.  Certain  habits,  on  the  other  hand, 
such  as  kissing,  which  probably  represents  the 
extension  of  a  habit  of  sexual  origin,  are  disad- 
vantageous and  infection  is  often  transmitted 
in  this  way.  In  syphilitic  infection  the  mouth 
forms  one  of  the  most  common  localizations 
of  the  disease  and  may  contain  the  causal  organ- 
isms in  great  numbers.  This,  the  spirochceta 
pallida,  is  an  organism  of  great  virulence,  and 
man  is  the  most  susceptible  animal.  The  dis- 
ease, like  gonorrhoea,  is  essentially  a  sexual  dis- 


194       DISEASE  AND  ITS  CAUSES 

ease,  the  primary  location  is  in  the  sexual  organs, 
and  it  is  transmitted  chiefly  by  sexual  contact. 
Of  all  the  infectious  diseases,  it  is  the  one  most 
frequently  transmitted  to  the  unborn  child;  in 
certain  cases  the  disease  is  transmitted,  in  others 
the  developing  foetus  may  be  so  injured  by  the 
toxic  products  of  the  disease  that  various  imperfec- 
tions of  development  result,  as  is  shown  in  deform- 
ities, or  in  conditions  which  render  the  entire 
organism  or  individual  organs,  particulariy  the 
nervous  system,  more  susceptible  to  injury. 
Following  the  primary  localization  of  the  ac- 
quired form  of  the  disease,  there  is  usually  second- 
ary localization  in  the  mucous  membrane  of 
the  mouth,  and  the  disease  may  be  transmitted 
by  kissing  or  by  the  use  of  contaminated  utensils. 
The  habit  of  indiscriminate  kissing  is  one  which 
might  with  great  benefit  be  given  up. 

There  is  definite  relation  between  age  and 
the  infectious  diseases.  In  general,  suscepti- 
bility is  increased  in  the  young;  young  animals 
can  be  successfully  inoculated  with  diseases  to 
which  the  adults  of  the  species  are  immune,  and 
certain  human  diseases,  such  as  scarlet  fever, 
measles  and  whooping  cough,  seem  to  be  the 
prerogatives  of  the  child.  It  must  be  remem- 
bered, however,  that  one  attack  of  these  diseases 
confers  a  strong  and  lasting  immunity  and 
children  represent  a  raw  material  unprotected 
by  previous  disease.     Where  measles  has  been 


DISEASE  AND   ITS  CAUSES        195 

introduced  into  an  island  population  for  the 
first  time,  all  ages  seem  equally  susceptible. 
All  ages  are  equally  susceptible  to  smallpox, 
and  yet  in  the  general  prevalence  of  the  disease  in 
the  prevaccination  period  it  was  almost  confined 
to  children,  the  adults  being  protected  by  a 
previous  attack.  The  habits  and  environment 
at  different  ages  have  an  influence  on  the  oppor- 
tunities for  infection.  There  is  comparatively 
little  opportunity  for  infection  during  the  first 
year,  in  which  period  the  infant  is  nursed  and 
has  a  narrow  environment  within  which  infection 
is  easily  controlled.  With  increasing  years  the 
opportunities  for  infection  increase.  When  the 
child  begins  to  move  and  crawl  on  hands  and 
knees  the  hands  become  contaminated,  and 
the  habit  of  putting  objects  handled  into  the 
mouth  makes  infection  by  this  route  possible. 
Food  also  becomes  more  varied,  milk  forms  an 
important  part  of  the  diet,  and  we  are  now  appre- 
ciating the  possibilities  of  raw  milk  in  conveying 
infection.  With  the  enlarging  environment, 
with  the  school  age  bringing  greater  contact 
of  the  child  with  others,  there  come  greater 
opportunities  for  infection  which  are  partly  offset 
by  the  increase  in  cleanliness.  The  dangers  of 
infection  in  the  school  period  are  now  greatly 
lessened  by  medical  inspection  and  care  of  the 
school  children.  In  the  small  epidemic  of  small- 
pox which  prevailed    in    Boston  from    1881    to 


196        DISEASE  AND  ITS  CAUSES 

1883,  there  was  a  sharp  decline  in  the  incidence 
of  the  disease  in  children  as  soon  as  the  school 
age  was  reached,  this  being  due  to  the  demand 
of  vaccination  as  a  condition  for  entrance  into 
the  schools.  Many  of  the  infectious  diseases 
are  much  milder  in  children  than  in  adults. 
This  is  the  case  in  typhoid  fever,  malaria  and 
yellow  fever.  The  comparative  immunity  of  the 
natives  to  yellow  fever  in  regions  where  this 
prevails  seems  to  be  due  to  their  having  acquired 
the  disease  in  infancy  in  so  mild  a  form  that  it 
was  not  recognized  as  such. 

The  infectious  diseases  are  preeminently  the 
diseases  of  the  first  third  of  life.  After  the  age 
of  forty  man  represents  a  select  material.  He 
has  acquired  immunity  to  many  infections  by 
having  experienced  them.  Habits  of  life  have 
become  fixed  and  there  is  a  general  adjustment  to 
enwonment.  The  only  infectious  disease  which 
shows  no  abatement  in  its  incidence  is  pneumonia, 
and  the  mortality  in  this  increases  with  age. 
Between  thirty-five  and  fifty-five  man  stands 
on  a  tolerably  firm  foundation  regarding  health; 
after  this  the  age  atrophies  begin,  the  effects  of 
previous  damage  begin  to  be  apparent,  and  the 
tumor  incidence  increases. 


CHAPTER  X 

Inheritance  as  a  Factor  in  Disease.  —  The  Process  of 
Cell    Multiplication.  —  The    Sexual    Cells    Differ 

FROM   THE   other    CeLLS    OF    THE    BoDY. INFECTION    OF 

THE  Ovum. — Intra-uterine  Infection.  —  The  Placenta 
AS  A  Barrier  to  Infection.  —  Variations  and  Muta- 
tions. —  Thf  Inheritance  of  Susceptibility  to  Dis- 
ease. —  The  Influence  of  Alcoholism  in  the  Parents 
ON  the  Descendants.  —  The  Heredity  of  Nervous  Dis- 
eases. —  Transmission  op  Disease  by  the  Female 
only.  —  Hemophilia.  —  The  Inheritance  of  Malfor- 
mations. —  The  Causes  of  Malformations.  —  Mater- 
nal Impressions  have  no  Influence.  —  Eugenics. 

The  question  of  inheritance  of  disease  is 
closely  associated  with  the  study  of  infection, 
and  the  general  subject  of  heredity  in  its  bearing 
on  disease  can  be  considered  here.  By  heredity 
is  understood  the  transference  of  similar  charac- 
teristics from  one  generation  of  organisms  to 
another.  The  formation  of  the  sexual  cells  is  a 
much  more  complex  process  than  that  of  the 
formation  of  single  differentiated  cells,  for  the 
properties  of  all  the  cells  of  the  body  are  repre- 
sented in  the  sexual  cells,  to  the  union  of  which 
the  heredity  transmission  of  the  qualities  of  the 
parents  is  due.  In  the  nucleus  of  all  the  cells 
in  the  body  there  is  a  material  called  chromatin, 
which  in  the  process  of  cell  division  forms  a 
197 


198        DISEASE  AND   ITS  CAUSES 

convoluted  thread;  this  afterwards  divides  into  a 
number  of  loops  called  chromosomes,  the  number 
of  which  are  constant  for  each  animal  species. 
In  cell  division  these  loops  divide  longitudinally, 
one-half  of  each  going  to  the  two  new  cells  which 
result  from  the  division;  each  new  cell  has  one-half 
of  all  the  chromatin  contained  in  the  old  and  also 


Fig.  21.  —  Diagram  showing  the  relation  of  the 
sexual  cells  to  the  somatic  cells  or  those  of  the  gen- 
ERAL BODY.  The  sexual  cells  are  represented  to  the  left  of 
the  line  at  the  bottom  of  diagram  and  are  black.  From  the 
fertilized  ovum  at  the  top  there  is  a  continuous  cell  develop- 
ment, with  diflferentiation  represented  in  the  cell  groups  of 
the  bottom  row.  It  is  seen  that  the  sexual  cells  are  formed 
directly  from  the  germ  cell  and  contain  no  admixture  from 
the  cells  of  the  body. 

one-half  of  the  cytoplasm  or  the  cell  material 
outside  of  the  nucleus.  The  process  of  sexual 
fertilization  consists  in  the  union  of  the  male 
and  female  sex  cells  and  an  equal  blending  of 
the  chromatin  contained  in  each  (Fig.  22).  In 
the  process  of  formation  of  the  sexual  cells  a 
diminution    of    the    number     of    chromosomes 


DISEASE  AND   ITS  CAUSES        199 

contained  in  them  takes  place,  but  this  is  pre- 
ceded by  such  an  intimate  intermingling  of  the 
chromatin  that  the  sexual  cells  contain  part  of 
all  the  chromosomes  of  the  undifferentiated  cells 
from  which  they  were  formed.  The  new  cell 
which  is  formed  by  the  union  of  the  male  and 
female  sexual  cells  and  which  constitutes  a  new 
organism,  contains  the  number  of  chromosomes 
characteristic  of  the  species  and  parts  of  all  the 
chromatin  of  the  undifferentiated  cells  of  male 
and  female  ancestors.  As  a  result  of  this  the 
most  complicated  mechanism  in  nature,  it  is  evi- 
dent that  in  a  strict  sense  there  can  be  no  here- 
dity of  a  disease  because  heredity  in  the  mammal 
is  solely  a  matter  of  the  chromosomes  and  these 
could  not  convey  a  parasite.  The  new  organism 
can,  however,  quickly  become  diseased  and,  by 
the  transference  of  disease  to  it  and  by  either 
parent,  there  is  the  appearance  of  hereditary  trans- 
mission of  disease,  though  in  reality  it  is  not  such. 
The  ovum  itself  can  become  the  site  of  infec- 
tion; this,  which  was  first  discovered  by  Pasteur 
in  the  eggs  of  silkworms,  takes  place  not  infre- 
quently in  the  infection  of  insects  with  pro- 
tozoa. In  Texas  fever  the  ticks  which  transmit 
the  disease,  after  filling  with  the  infected  blood, 
drop  off  and  lay  eggs  which  contain  the  parasites, 
and  the  disease  is  propagated  by  the  young 
ticks  in  whom  the  parasites  have  multiplied. 
The  same  thing  is  true  in  regard  to  the  African 


200        DISEASE  AND   ITS  CAUSES 

relapsing  or  tick  fever,  which  is  also  transferred 
by  a  tick.  In  the  white  diarrhoea  of  chickens 
the  eggs  become  infected  before  they  are  laid 
and  the  young  chick  is  infected  before  it  emerges 
from  the  shell.  It  is  highly  improbable,  and 
there  is  no  certain  evidence  for  it,  that  the 
extremely  small  amount  of  material  contributed 
by  the  male  can  become  infected  and  bring 
infection  to  the  new  organism.  In  the  cases 
in  which  disease  of  the  male  parent  is  trans- 
ferred to  the  offspring,  it  is  either  by  an  in- 
fection of  the  female  by  the  male,  with 
transference  of  the  infection  from  her  to  the 
developing  organism,  or  with  the  male  sexual 
cells  there  may  be  a  transference  to  the  female 
of  the  infectious  material  and  the  new  organism 
may  be  directly  infected.  No  other  disease  in 
man  is  so  easily  and  directly  transferred  from 
either  parent  to  offspring  as  is  syphilis,  and  the 
disease  is  extremely  malignant  for  the  foetus, 
usually  causing  death  before  the  normal  period 
of  intra-uterine  development  is  reached. 

The  mother  gives  the  protection  of  a  narrow 
and  unchanging  environment  and  food  to  the 
new  organism  which  develops  within  the  uterus, 
and  there  is  always  a  membranous  separation 
between  them.  Disease  of  the  mother  may 
affect  the  foetus  in  a  number  of  ways.  In  most 
cases  the  membrane  of  separation  is  an  eflScient 
guard  preventing  pathogenic  organisms  reaching 


DISEASE  AND   ITS   CAUSES 


201 


Fig.  22.  —  Diagrammatic  representation  of  the  pro- 
cess OF  FERTILIZATION.  (IJoveri.)  Ill  the  first  cell  (a)  the 
ovum  is  shown  in  process  of  fertilization  by  the  entering  sper- 
matozoon or  male  sexual  element.  In  the  following  cells  there 
is  shown  the  increase  in  amount  of  the  male  material  and  the 
final  intimate  commingling  in  g  which  precedes  the  first  seg- 
mentation, g  represents  a  new  organism  formed  by  the  union 
of  tlie  male  or  female  cell  but  differing  from  either  of  them. 


202        DISEASE  AND   ITS  CAUSES 

the  foetus  from  the  mother.  In  certain  cases, 
however,  the  guard  can  be  passed.  In  small- 
pox, not  infrequently,  the  disease  extends  from 
the  mother  to  the  foetus,  and  the  child  may  die 
of  the  infection  or  be  bom  at  term  with  the  scars 
resulting  from  the  disease  upon  it.  Syphilis 
in  the  mother  in  an  active  stage  is  practically 
always  extended  to  the  foetus.  We  have  said 
that  in  an  infectious  disease  substances  of  an 
injurious  character  are  produced  by  bacteria, 
and  such  substances  being  in  solution  in  the 
blood  of  the  infected  mother  can  pass  through 
the  membranous  barrier  and  may  destroy  the 
foetus  although  the  mother  recovers  from  the 
infection. 

Living  matter  is  always  indi\adual,  and  this 
individuality  is  expressed  in  slight  structural  va- 
riations from  the  type  of  the  species  as  shown 
in  an  average  of  measurements,  and  also  in  slight 
variations  in  function  or  the  reactions  which 
living  tissue  shows  towards  the  conditions  act- 
ing upon  it.  The  anatomical  variations  are  more 
striking  because  they  can  be  demonstrated  by 
weight  and  measure,  but  the  functional  varia- 
tions are  equally  numerous.  Thus,  no  two 
brains  react  in  exactly  the  same  way  to  the 
impressions  received  by  the  sense  organs;  there 
are  differences  in  muscular  action,  differences 
in  digestion;  these  variations  in  function  are 
due  to  variations  in  the  structure  of  living  ma- 


DISEASE  AND  ITS  CAUSES        203 

terial  which  are  too  minute  for  our  compara- 
tively coarse  methods  of  detection.  In  the 
enormous  complexity  of  living  matter  it  is  im- 
possible that  there  should  not  be  minute  differ- 
ences in  molecular  arrangement  and  to  this  such 
functional  variations  may  be  due.  Chemistry 
gives  us  a  number  of  examples  of  variations  in  the 
reaction  of  substances  which  with  the  same  com- 
position differ  in  the  molecular  arrangement. 
Even  in  so  simple  a  mechanism  as  a  watch 
there  are  slight  differences  in  structure  which 
gives  to  each  watch  certain  individual  charac- 
teristics, but  the  type  as  an  instrument  con- 
structed for  recording  time  remains.  In  the 
fusion  of  the  chromosomes  of  the  male  and 
female  sexual  cells,  to  which  the  hereditary 
transmission  of  the  ancestral  qualities  to  the 
new  offspring  is  due,  there  are  differences'  in 
the  qualities  of  each,  for  the  individuality  of  the 
parents  is  expressed  in  the  germ  cells,  and 
the  varying  way  in  which  these  may  fuse  gives  to 
the  new  cell  qualities  of  its  own  in  addition  to 
qualities  which  come  from  each  ancestor,  and 
from  remote  ancestors  through  these.  The 
qualities  with  which  the  new  organism  starts 
are  those  which  it  has  received  from  its  ancestors 
plus  its  individuality.  The  fact  that  the  sexual 
cells  are  formed  from  the  early  formed  cells  of 
the  new  organism  which  represent  all  of  the  qual- 
ities of  the  fertilized  ovum  or  primordial  cell, 


204        DISEASE  AND   ITS  CAUSES 

renders  it  unlikely  that  the  new  oflFspring  will 
contain  qualities  which  the  parents  have  acquired. 
The  question  of  the  inheritance  of  characteristics 
which  the  parents  have  acquired  as  the  result 
of  the  action  of  environment  upon  them  is  one 
which  is  still  actively  investigated  by  the  students 
of  heredity,  but  the  weight  of  evidence  is  op- 
posed to  this  belief. 

In  the  new  organism  the  type  of  the  species  is 
preserved  and  the  variations  from  the  mean  to 
which  individuality  is  due  are  slight.  We  are 
accustomed  to  regard  as  variations  somewhat 
greater  departures  from  the  species  type  than  is 
represented  in  individuality,  but  there  is  no 
sharp  dividing  line  between  them. 

Very  much  wider  departures  from  the  species 
type  are  known  as  mutations.  Such  variations 
and  mutations,  like  individuality,  may  be  ex- 
pressed in  qualities  which  can  be  weighed  and 
measured,  or  in  function,  and  all  these  can  be 
inherited;  certain  of  them  known  as  dominant 
characteristics  more  readily  than  others,  which 
are  known  as  recessive.  If  these  variations 
from  the  type  are  advantageous,  they  may  be 
preserved  and  become  the  property  of  the  species, 
and  it  is  in  this  way  that  the  characteristics  of 
the  different  races  have  arisen.  Certain  of  the 
variations  are  unfavorable  to  the  race.  The 
varying  predisposition  to  infection  which  un- 
doubtedly exists  and  may  be  inherited  represents 


DISEASE  AND   ITS  CAUSES        205 

such  a  variation.  Tuberculosis  is  an  instance  of 
this;  for,  while  the  cause  of  the  disease  is  the 
tubercle  bacillus,  there  is  enormous  difference  in 
the  resistance  of  the  body  to  its  action  in  different 
individuals.  The  disease  is  to  a  considerable 
extent  one  of  families,  but  while  this  is  true 
the  degree  of  the  influence  exerted  by  heredity 
can  be  greatly  overestimated.  The  disease  is 
so  common  that  in  tracing  the  ancestry  of  tuber- 
culous patients  it  is  rare  to  find  the  disease  not 
represented  in  the  ancestors.  A  further  difficulty 
is  that  the  environment  is  also  inherited.  The 
child  of  a  tuberculous  parent  has  much  better 
opportunity  to  acquire  the  infection  than  a  child 
without  such  an  environment  [page  167].  Other 
diseases  than  the  infectious  seem  to  be  inherited, 
of  which  gout  is  an  example.  In  gout  there  is 
an  unusual  action  of  the  cells  of  the  body  which 
leads  to  the  formation  and  the  retention  in  the 
body  of  substances  which  are  injurious.  Here  it  is 
not  the  disease  which  is  inherited,  but  the  vari- 
ation in  structure  to  which  the  unusual  and 
injurious  action  of  the  cells  is  due. 

While  tuberculosis  and  gout  represent  in- 
stances in  which,  although  the  disease  itself 
is  not  inherited  yet  the  presence  of  the  disease 
in  the  ascendants  so  affects  the  germinal  material 
that  the  offspring  is  more  susceptible  to  these 
particular  diseases,  much  more  common  are  the 
cases  in  which  disease  in  the  parents  produces  a 


206        DISEASE  AND   ITS  CAUSES 

defective  offspring,  the  defect  consisting  in  a 
general  loss  of  resistance  manifested  in  a  variety 
of  ways,  but  not  necessarily  repeating  the  dis- 
eased condition  of  the  parent.  In  these  cases 
the  disease  in  the  parents  affects  all  the  cells  of 
the  body  including  the  germinal  cells,  and  the 
defective  qualities  in  the  germ  cells  will  affect 
the  cells  of  the  offspring  which  are  derived  from 
these.  There  is  a  tendency  in  these  cases  to  the 
repetition  in  the  offspring  of  the  disease  of 
the  parents,  because  the  particular  form  of  the 
parental  disease  may  have  been  due  to  or  in- 
fluenced by  variation  of  structure.  One  of  the 
best  examples  of  affection  of  the  offspring  by 
diseased  conditions  of  the  parents  produced  by 
a  toxic  agent  which  directly  or  indirectly  affects 
all  the  cells  of  the  body  is  afforded  by  alcohol 
when  used  in  excess.  Since  drunkenness  has 
become  a  medical  rather  than  a  moral  question,  a 
great  deal  of  reliable  data  has  accumulated  in 
regard  to  it  as  a  factor  in  the  heredity  of  disease. 
Grotjahn  gives  the  following  examples:  Six 
families  were  investigated  in  which  there  were 
thirty-one  children.  In  all  these  families  the 
father  and  grandfather  on  the  father's  side  were 
chronic  alcoholics,  and  in  certain  of  the  families 
drunkenness  prevailed  in  the  more  remote 
ancestors.  The  following  was  the  fate  of  the 
children :  eight  died  shortly  after  birth  of  general 
weakness,  seven  died  of  convulsions  in  the  first 


DISEASE  AND   ITS  CAUSES        207 

month,  three  were  malformed,  three  were  idiotic, 
three  were  feeble-minded,  three  were  dwarfs, 
three  were  epileptics,  two  were  normal.  In  a 
second  group  of  three  families  there  were  twenty 
children.  The  fathers  were  drunkards,  but 
their  immediate  ancestors  were  free :  four  children 
died  of  general  weakness,  three  of  convulsions 
in  the  first  month,  two  were  feeble-minded,  one 
was  a  dwarf,  one  was  an  epileptic,  seven  were  nor- 
mal. In  a  family  in  which  both  father  and  mother 
and  their  ancestors  were  drunkards  there  were 
six  children:  three  died  of  convulsions  within 
six  months,  one  was  an  idiot,  one  a  dwarf,  and  one 
an  epileptic.  For  comparison  there  were  taken 
from  the  same  station  in  life  ten  families  in  which 
there  was  no  drunkenness:  three  children  died 
from  general  weakness,  three  from  intestinal 
troubles,  two  of  nervous  affection,  two  were  feeble- 
minded, two  were  malformed,  fifty  were  normal. 
Legrain  has  studied  on  a  larger  scale  the  de- 
scendants of  two  hundred  and  fifteen  families 
of  drunkards  in  which  there  were  eight  hundred 
and  nineteen  children.  One  hundred  and  forty- 
five  of  these  were  insane,  sixty -two  were  criminals, 
and  one  hundred  and  ninety -seven  drunkards. 
Of  course  all  this  cannot  be  attributed  to  alcohol 
alone.  There  is  first  to  be  considered  a  probable 
variation  in  the  nervous  system  which  is  ex- 
pressed in  the  alcoholic  habit;  second,  the  en- 
vironment consisting  in  poverty,  bad  associates. 


208       DISEASE  AND  ITS  CAUSES 

etc.,  which  the  alcoholic  habit  brings;  third, 
the  alcohol  alone.  That  defective  inheritance 
so  frequently  takes  the  form  of  alcoholism  is 
largely  due  to  the  environment.  There  has  never 
been  the  opportunity  to  study  on  a  large  scale 
the  eflfect  of  the  complete  deprivation  of  alcohol 
from  a  people  living  in  the  environment  of  modem 
civilization.  There  is  a  possibility,  and  even 
probability,  that  the  defective  nervous  organ- 
ization which  predisposes  to  alcoholism  would 
seek  satisfaction  in  the  use  of  some  other 
sedative  drug.  So  complex  are  all  the  inter- 
relations of  the  social  system  that  it  would 
be  possible  to  regard  alcohol  as  an  agent  use- 
ful in  removing  the  defective,  were  it  not  for 
its  long-enduring  action  and  its  effects  on  the 
descendants,  procreation  not  being  affected  by 
its  use. 

Diseases  of  the  nervous  system  are  particu- 
larly apt  to  affect  the  offspring,  and  often  the 
inherited  condition  repeats  that  of  the  parents. 
This  is  due  to  the  fact  that  most  of  the  nervous 
diseases  depend  both  upon  intrinsic  factors  which 
consist  in  some  defective  condition  of  the  nervous 
system  representing  a  variation,  and  extrinsic 
factors  due  to  environment  or  occupation  which 
make  the  basal  condition  operative.  The  definite 
relation  between  alcoholism  and  insanity  is  due  to 
alcohol  acting  not  as  an  intrinsic  but  an  extrinsic 
factor,  bringing  into  effectiveness  the  hereditary 


DISEASE  AND   ITS  CAUSES        209 

weakness  of  the  nervous  system.  The  influence 
of  heredity  in  producing  insanity  is  variously 
estimated  at  from  twenty-six  per  cent  to  sixty 
per  cent  of  all  cases.  This  great  difference  in 
the  estimation  of  the  hereditary  influence  is 
due  to  the  personal  equation  of  the  statistician, 
and  the  care  with  which  other  factors  are  elimi- 
nated. In  the  more  severe  form  of  the  hereditary 
degeneration  the  same  pathological  conditions 
are  repeated  in  the  descendants.  In  certain 
cases  the  severity  of  the  condition  increases 
from  generation  to  generation.  According  to 
Morel  there  may  be  merely  what  is  recognized 
as  a  nervous  temperament  often  associated 
with  moral  depravity  and  various  excesses  in 
the  first  generation;  in  the  second,  severe  neu- 
roses, a  tendency  to  apoplexy  and  alcoholism; 
in  the  third,  psychic  disturbances,  suicidal 
tendencies  and  intellectual  incapacity;  and  in 
the  fourth,  congenital  idiocy,  malformations 
and  arrests  of  development.  There  are  some 
very  definite  data  with  regard  to  inheritance 
in  the  nervous  disease  known  as  epilepsy.  The 
essential  condition  in  this  consists  in  attacks 
of  unconsciousness,  usually  accompanied  by  a 
discharge  of  nerve  force  shown  in  convulsions, 
the  attack  being  often  preceded  by  peculiar 
sensations  of  some  sort  known  as  the  aura.  In 
the  most  marked  forms  of  the  affection  heredity 
plays  but  little  part,  owing  to  the  early  super- 


210       DISEASE  AND   ITS  CAUSES 

vention  of  imbecility  and  helplessness,  and  it 
is  a  greater  factor  in  the  better  classes  of  society 
than  in  the  proletariat.  In  the  better  classes, 
owing  to  the  greater  care  of  the  cases  and  the 
avoidance  of  exciting  causes  of  the  attacks,  the 
disease  is  better  controlled  and  rarely  advances 
to  the  extent  that  it  does  among  the  poor.  The 
association  of  epilepsy  and  alcoholism  is  espe- 
cially dangerous,  for  a  slight  amount  of  alcohol 
may  greatly  accentuate  the  disease.  In  five 
hundred  and  thirty -five  children  in  whose  parent- 
age there  were  sixty-two  male  and  seventy-four 
female  epileptics,  twenty-two  were  born  dead,  one 
hundred  and  ninety-five  died  from  convulsions 
in  infancy,  twenty-seven  died  in  infancy  from 
other  causes,  seventy-eight  were  epileptics,  eleven 
were  insane,  thirty-nine  were  paralyzed,  forty- 
five  were  hysterical,  six  had  St.  Vitus's  dance, 
one  hundred  and  five  were  ordinarily  healthy. 
That  variations  in  the  nervous  system  which 
produce  more  or  less  unusual  mental  peculiarities 
and  which  do  not  take  the  form  of  nervous 
disease  are  inherited,  the  most  superficial  con- 
sideration shows.  A  child  in  its  mental  character- 
istics is  said  to  take  after  one  or  the  other  of  its 
parents,  certain  habits  and  mental  traits  are  the 
same,  often  even  the  handwriting  of  a  child 
resembles  that  of  a  parent. 

In  certain  cases  the  inheritance  is  transmitted 
by  the  female  alone.     This  is  the  case  in  the 


DISEASE  AND   ITS   CAUSES        211 

haemophilia,  the  unfortunate  subjects  of  which  are 
known  as  bleeders.  There  is  in  this  a  marked 
tendency  to  haemorrhage  which  depends  upon  an 
alteration  in  the  character  of  the  blood  which 
prevents  clotting.  This,  the  natural  means  of 
stopping  bleeding  from  small  wounds,  being  in 
abeyance,  fatal  haemorrhage  may  result  from 
pulling  a  tooth  or  from  an  insignificant  wound. 
There  is  a  seeming  injustice  in  the  inheritance, 
for  the  females  do  not  suffer  from  the  disease 
although  they  transmit  it,  while  the  males  who 
have  the  disease  cannot  even  create  additional 
sympathy  by  transmitting  it. 

The  most  obvious  inheritance  is  seen  in  the 
case  of  malformations.  These  represent  wide 
departures  from  the  type  of  the  species  as  repre- 
sented in  the  form.  There  is  no  hard  and  fast 
line  separating  the  slight  departures  from  the  nor- 
mal type  known  as  variations  and  mutations, 
from  the  malformations.  Certain  of  the  malforma- 
tions known  as  monstrosities  hardly  represent  the 
human  type.  These  are  the  cases  in  which  the 
foetus  is  represented  in  a  formless  mass  of  tissue, 
or  there  is  absence  of  development  of  important 
parts  such  as  the  nervous  system  or  there  is  more 
or  less  extensive  duplication  of  the  body.  There 
has  always  been  a  great  deal  of  popular  interest 
attached  to  the  malformations  owing  to  the  part 
which  maternal  impressions  are  supposed  to 
play  in  their  production.    In  this,  some  striking 


212       DISEASE  AND   ITS  CAUSES 

impression  made  on  the  pregnant  woman  is 
supposed  to  affect  in  a  definite  way  the  structure 
of  the  child.  The  cases,  for  instance,  in  which 
a  woman  sees  an  accident  involving  a  wound 
or  a  loss  of  an  arm  and  the  child  at  birth  shows 
a  malformation  involving  the  same  part.  There 
is  no  association  between  maternal  impressions 
and  malformations,  although  there  have  been 
many  striking  coincidences.  All  malformations 
arise  during  the  first  six  weeks  of  pregnancy 
known  as  the  embryonic  period,  in  which  the 
development  of  the  form  of  the  child  is  taking 
place,  and  during  which  time  there  is  little  con- 
sciousness of  pregnancy.  Maternal  impressions 
are  usually  received  at  a  later  period,  when  the 
form  of  the  child  is  complete  and  it  is  merely 
growing.  It  must  be  remembered  also  that 
there  is  neither  nervous  nor  vascular  connection 
between  the  child  in  the  uterus  and  the  mother, 
the  child  being  from  the  period  of  conception 
an  independent  entity  to  which  the  mother 
gives  nutriment  merely.  Of  course,  as  has  been 
said,  the  mother  may  transmit  to  the  child  sub- 
stances which  are  injurious,  and  in  certain  cases 
parasites  may  pass  from  the  mother  to  the  foetus. 
The  same  types  of  malformations  which  occur  in 
man  are  also  seen  in  birds,  and  it  would  require 
a  more  vigorous  imagination  than  is  usual  to 
believe  that  a  brooding  hen  could  transmit  an 
impression  to  an  egg  and  that  a  headless  chick 


DISEASE  AND   ITS  CAUSES        213 

could  result  from  witnessing  the  sacrifice  of  an 
associate.  The  idea  of  the  importance  of  maternal 
impressions  in  influencing  the  character  of  the 
offspring  is  a  very  old  one,  a  well-known  instance 
being  the  sharp  practice  of  Jacob's  using  peeled 
wands  to  influence  the  color  of  his  cattle.  In 
regard  to  coincidences  the  great  number  of 
cases  in  which  strong  impressions  made  on 
the  mind  of  the  pregnant  mother  without  result 
on  the  offspring  are  forgotten.  The  belief  has 
been  productive  of  great  anxiety  and  even 
unhappiness  during  a  period  which  is  necessarily 
a  trying  one,  and  should  be  dismissed  as  being 
both  theoretically  impossible  and  unsupported 
by  fact. 

The  malformations  are  divided  anatomically 
into  those  characterized,  first,  by  excess  forma* 
tion,  second,  by  deficient  formation,  third,  by 
abnormal  displacement  of  parts.  They  are  due 
to  intrinsic  causes  which  are  in  the  germ,  and 
which  may  be  due  to  some  unusual  conditions 
in  either  the  male  or  female  germ  cell  or  an 
imperfect  commingling  of  the  germinal  material, 
and  to  extrinsic  causes  which  physically,  as  in 
the  nature  of  a  shock  or  chemically  as  by  the  ac- 
tion of  a  poison,  may  affect  the  embryo  through 
the  mother.  Malformations  are  made  more 
numerous  in  chickens  by  shaking  the  eggs  before 
brooding.  A  number  of  malformations  are  pro- 
duced  by   accidental   conditions   arising  in  the 


214       DISEASE  AND  ITS  CAUSES 

environment;  for  instance,  the  vascular  cord  con- 
necting mother  and  child  may  become  wound 
around  parts  constricting  them  or  even  cutting 
them  off,  and  the  membrane  around  the  child 
may  become  adherent  to  certain  parts  and  pre- 
vent the  development  of  these.  The  extrinsic 
causes  are  more  operative  the  more  unfavorable 
is  the  environment  of  the  mother.  Malforma- 
tions are  more  common  in  illegitimate  children 
than  in  legitimate  and  more  common  in  alcoholic 
mothers;  there  is  an  unfavorable  environment  of 
poverty  in  both  cases,  added  to  in  the  latter  and 
usually  in  the  former  by  the  injurious  action 
of  the  alcohol. 

The  more  extensive  malformations  have  no 
effect  on  heredity,  because  the  subjects  of  them 
are  incapable  of  procreation.  The  malformations 
which  arise  from  the  accidents  of  pregnancy 
and  which  are  compatible  with  a  perfectly 
normal  germ  are  in  the  nature  of  acquired 
characteristics  and  are  not  inherited.  Those 
malformations,  however,  which  are  due  to 
qualities  in  the  germinal  material  itself  are 
inherited,  and  certain  of  them  with  remarkable 
persistence.  There  are  instances  in  which  the 
slight  malformation  consisting  in  an  excess  of 
fingers  or  toes  has  persisted  through  many 
generations.  It  may  occasionally  lapse  in  a 
generation  to  reappear  later.  In  certain  cases, 
notably  in  the  bleeders,  the  inheritance  is  trans- 


DISEASE  AND   ITS  CAUSES        215 

mitted  by  the  female  alone,  in  other  cases  by  the 
sexes  equally,  but  there  are  no  cases  of  trans- 
mission by  the  male  line  only.  It  is  evident 
that  when  the  same  malformation  affects  both 
the  male  and  the  female  line  the  hereditary 
influence  is  much  stronger.  A  case  has  been 
related  to  me  in  which  most  of  the  inhabitants 
in  a  remote  mountain  valley  in  Virginia  where 
there  has  been  much  intermarriage  have  one 
of  the  joints  of  the  fingers  missing.  There  is  a 
very  prevalent  idea  that  in  close  intermarriage 
in  families  variations  and  malformations  often 
unfortunate  for  the  individual  are  more  common. 
All  experimental  evidence  obtained  by  inter- 
breeding of  animals  shows  that  close  interbreed- 
ing is  not  productive  of  variation,  but  that 
variations  existing  in  the  breed  become  ac- 
centuated. Variations  either  advantageous  or 
disadvantageous  for  the  race  or  individual  may 
either  of  them  become  more  prevalent  by 
close  intermarriage.  It  seems,  however,  to  have 
been  shown  by  the  customs  of  the  human 
race  that  very  close  intermarriage  is  disadvan- 
tageous. 

Eugenics,  which  signifies  an  attempt  at  the 
betterment  of  the  race  by  the  avoidance  of  bad 
heredity,  has  within  recent  years  attracted  much 
attention  and  is  of  importance.  Some  of  its 
advocates  have  become  so  enthusiastic  as  to 
believe    that    it    will    be    possible    to    breed 


216        DISEASE  AND   ITS  CAUSES 

men  as  cattle  and  ultimately  to  produce  a  race 
ideally  perfect.  It  is  true  that  by  careful 
selection  and  regulation  of  marriage  certain 
variations,  whether  relating  to  coarse  bodily 
form  or  to  the  less  obvious  changes  denoted  by 
function,  can  be  perpetuated  and  strengthened. 
That  the  Semitic  race  excels  in  commerce  is 
probably  due  to  the  fact  that  the  variation  of 
the  brain  which  affected  favorably  the  mental 
action  conducive  to  this  form  of  activity,  was 
favorable  for  the  race  in  the  hostile  environment 
in  which  it  was  usually  placed  and  transmitted 
and  strengthened  by  clbse  intermarriage.  It 
is  impossible,  however,  to  form  a  conception  of 
what  may  be  regarded  as  an  ideal  type  of  the 
human  species.  The  type  which  might  be  ideal 
in  a  certain  environment  might  not  be  ideal  in 
another,  and  environment  is  probably  of  equal 
importance  with  the  material.  The  eugenics 
movement  has  enormously  stimulated  research 
into  heredity  by  the  methods  both  of  animal 
experimentation  and  observation,  and  study  of 
heredity  in  man.  As  in  all  of  the  beginning 
sciences  there  is  not  the  close  inter-relation  of 
observed  facts  and  theory,  but  there  is  excess  of 
theory  and  dearth  of  facts.  Certain  considera- 
tions, however,  seem  to  be  evident.  It  would 
seem  to  be  evident  that  individuals  should  be 
healthy  and  enabled  to  maintain  themselves  in 
the  environment  in  which  they  are  placed,  but 


DISEASE   AND   ITS  CAUSES        217 

the  qualities  which  may  enable  an  individual 
successfully  to  adapt  himself  to  factory  life,  or 
life  in  the  crowds  and  strong  competition  of  the 
city,  may  not  be,  and  probably  are  not,  qualities 
which  are  good  for  the  race  in  general  or  for 
his  unmediate  descendants.  At  present  our 
attempts  to  influence  heredity  should  be  limited 
to  the  heredity  of  disease  only.  We  can  cer- 
tainly say  that  intermarriage  between  persons 
who  have  tuberculosis  or  in  whose  families  the 
disease  has  prevailed  is  disadvantageous  for  the 
offspring;  the  same  holds  true  for  insanity  and 
for  nervous  diseases  of  all  sorts,  for  forms  of 
criminality,  for  alcoholism,  and  for  those  diseases 
which  are  long  enduring  and  transmitted  by 
sexual  contact  such  as  syphilis  and  gonorrhoea. 
It  is  of  importance  that  the  facts  bearing  on 
the  hereditary  transmission  of  disease  should 
become  of  general  knowledge,  in  order  that  the 
dangers  may  be  known  and  voluntarily  avoided. 
No  measures  of  preventive  medicine  are  suc- 
cessful which  are  not  supported  by  a  public 
educated  to  appreciate  their  importance,  and  the 
same  holds  true  of  eugenics.  How  successful 
will  be  public  measures  leading  to  the  prevention 
of  offspring  in  the  obviously  unfit  by  sterilization 
of  both  males  and  females  is  uncertain.  It  is 
doubtful  whether  public  sentiment  at  the  present 
time  will  allow  the  measure  to  be  thoroughly 
carried  out.     Some  results  in  preventing  unfit 


218        DISEASE  AND   ITS  CAUSES 

heredity  may  be  attained  by  the  greater  ex- 
tension of  asylum  life,  but  the  additional  burden 
of  this  upon  the  labor  of  the  people  would  be 
difficult  to  bear.  At  best  such  measures  would 
only  be  carried  out  in  the  lower  class  of  society. 


CHAPTER  XI 

Chronic  Diseases.  —  Disease  of  the  Heart  as  an  Ex- 
ample. —  The  Structure  and  Function  of  the  Heart. 
— The  Action  of  the  Valves.  —  The  Production  op 
Heart  Disease  by  Infection.  —  The  Conditions  Pro- 
duced IN  the  Valves.  —  The  Manner  in  which 
Disease  of  the  Valves  Interferes  with  their  Func- 
tion. —  The  Compensation  of  Injury  by  Increased 
Action  of  Heart.  —  The  Enlargement  of  the  Heart. 
— The  Result  of  Imperfect  Work  of  the  Heart.  — 
— Venous  Congestion.  —  Dropsy.  —  Chronic  Disease  of 
the  Nervous  System.  —  Insanity.  —  Relation  between 
Insanity  and  Criminality.  —  Alcoholism  and  Syphilis 

FREQUENT  CaUSES  OF  INSANITY. ThE  DiRECT  AND  IN- 
DIRECT Causes  of  Nervous  Diseases.  —  The  Relation 
BETWEEN  Social  Life  and  Nervous  Diseases.  —  Func- 
tional AND  Organic  Disease.  —  Neurasthenia. 

Chronic  diseases  are  diseases  of  long  duration 
and  which  do  not  tend  to  result  in  complete 
recovery;  in  certain  cases  a  cause  of  disease 
persists  in  the  body  producing  constant  damage, 
or  in  the  course  of  disease  some  organ  or  organs 
of  the  body  are  damaged  beyond  the  capacity 
of  repair,  and  the  imperfect  action  of  such  dam- 
aged organs  interferes  wath  the  harmonious . 
inter-relation  of  organs  and  the  general  well- 
being  of  the  body.  The  effect  of  damage  in 
producing  chronic  disease  may  not  appear  at 
once,  for  the  great  power  of  adaptation  of  organs 
219 


220        DISEASE  AND  ITS  CAUSES 

and  the  exercise  of  reserve  force  may  for  a  time 
render  the  damage  imperceptible;  when,  however, 
age  or  the  supervention  of  further  injury  dimin- 
ishes the  power  of  adaptation  the  condition 
of  disease  becomes  evident.  Chronic  disease 
may  be  caused  by  parasites  when  the  relation 
between  host  and  parasite  is  not  in  high  degree 
inimical,  as  in  tuberculosis,  gonorrhoea,  syphilis, 
most  of  the  trypanosome  diseases  and  the  dis- 
eases produced  by  the  higher  parasites.  In 
certain  cases  the  chronic  disease  represents 
really  a  series  of  acute  onsets;  thus  in  the  case 
of  the  parasites  there  may  be  periods  of  complete 
quiescence  of  infection  but  not  recovery,  the 
parasites  remaining  in  the  body  and  attack- 
ing when  the  defences  of  the  body  are  in 
some  way  weakened.  In  such  cases  there  may 
be  temporary  immunity  produced  by  each  ex- 
cursion of  the  disease,  but  the  immunity  is  not 
permanent  nor  is  the  parasite  destroyed.  There 
is  a  further  connection  between  chronic  dis- 
ease and  infection  in  that  the  damage  to  the 
organs,  which  is  the  great  factor  underly- 
ing chronic  disease,  is  so  often  the  result  of  an 
.  infection. 

The  infectious  diseases  are  those  of  early  hfe; 
chronic  disease,  on  the  other  hand,  is  most  com- 
mon in  the  latter  third  of  life.  This  is  due  to 
the  fact  that  in  consequence  of  the  general  wear 
of   the   body   this   becomes   less    resistant,    less 


DISEASE  AND   ITS  CAUSES        221 

capable  of  adaptation,  and  organic  injury,  which 
in  the  younger  individual  would  be  in  some  way 
compensated  for,  becomes  operative.  The  terri- 
tory of  chronic  disease  is  so  vast  that  not  even  a 
superficial  review  of  the  diseases  coming  under 
this  category  can  be  attempted  in  the  limits  of 
this  book,  and  it  will  be  best  to  give  single 
examples  only,  for  the  same  general  principles 
apply  to  all.  One  of  the  best  examples  is  given 
in  chronic  disease  of  the  heart. 

The  heart  is  a  hollow  organ  forming  a  part  of 
the  blood  vascular  system  and  serving  to  give 
motion  to  the  blood  within  the  vessels  by  the 
contraction  of  its  strong  muscular  walls.  It  is 
essentially  a  pump,  and,  as  in  a  pump,  the  direc- 
tion which  the  fluid  takes  when  forced  out  of 
its  cavity  by  the  contraction  of  the  walls  dimin- 
ishing or  closing  the  cavity  space,  is  determined 
by  valves.  The  contraction  of  the  heart,  which 
takes  place  seventy  to  eighty  times  in  a  minute, 
is  automatic  and  is  due  to  the  essential  quality  of 
the  muscle  which  composes  it.  The  character, 
frequency  and  force  of  contraction,  however,  can 
be  influenced  by  the  nervous  system  and  by  the 
direct  action  of  substances  upon  the  heart  muscle. 
The  heart  is  divided  by  a  longitudinal  partition 
into  a  right  and  left  cavity,  and  these  cavities 
are  divided  by  transverse  septa,  with  openings 
in  them  controlled  by  valves,  each  into  two 
chambers    termed-  auricle    and   ventricle.     The 


222       DISEASE  AND   ITS  CAUSES 

auricle  and  ventricle  on  each  side  are  completely 
separated. 

The  circulation  of  the  blood  through  the  heart 
is  as  follows:  The  blood,  which  in  the  veins  of 
the  body  is  flowing  towards  the  Tieart,  passes 
by  two  channels,  which  respectively  receive  the 
blood  from  the  upper  and  lower  part  of  the 
body,  into  the  right  auricle.  WTien  this  becomes 
distended  it  contracts,  forcing  the  blood  into 
the  right  ventricle;  the  ventricle  then  contracts 
and  sends  the  blood  into  the  arteries  of  the  lungs, 
the  passage  of  blood  into  the  auricle  being  pre- 
vented by  valves  which  close  the  opening  between 
auricle  and  ventricle  when  the  latter  contracts 
upon  its  contents.  When  the  ventricle  empties 
by  its  contraction  the  wall  relaxes  and  the  back 
flow  from  the  artery  is  prevented  by  crescentic- 
shaped  valves  placed  where  the  artery  joins  the 
ventricle.  A  similar  arrangement  of  valves  is 
on  the  left  side  of  the  heart.  The  pressure  given 
the  blood  by  the  contraction  of  the  right  ven- 
tricle sends  it  through  the  lungs;  from  these, 
after  it  has  been  oxygenated,  it  passes  into  the 
left  auricle,  then  into  the  left  ventricle  and  from 
this  into  the  great  artery  of  the  body,  the  aorta, 
which  gives  off  branches  supplying  the  capil- 
laries of  all  parts  of  the  body.  Both  of  the 
auricles  and  both  of  the  ventricles  contract  at 
the  same  time,  the  ventricular  contraction  fol- 
lowing   closely    upon    the    contraction    of    the 


DISEASE  AND   ITS   CAUSES        223 

auricles.  Contraction  or  systole  is  followed  by 
a  pause  or  diastole  during  which  the  blood  flows 
from  the  veins  into  the  auricles.  The  work 
which  the  right  ventricle  accomplishes  is  very 
much  less  than  that  of  the  left,  and  the  right 
ventricle  has  a  correspondingly  thinner  wall. 
The  size  of  the  heart  is  influenced  by  the  size  and 
the  occupation  of  the  individual  being  larger 
in  the  large  individual  than  in  the  small,  and 
larger  in  the  active  and  vigorous  than  in  the 
inactive.  Generally  speaking,  the  heart  is  about 
as  large  as  the  closed  fist  of  its  possessor. 

Imperfections  of  the  heart  which  interfere 
with  its  action  may  be  the  result  of  failure  of 
development  or  disease.  An  imperfect  heart 
which  can,  however,  fully  meet  the  limited 
demands  made  upon  it  in  intra-uterine  life, 
may  be  incapable  of  the  work  placed  upon  it 
in  extra-uterine  life.  Children  with  imperfectly 
formed  hearts  may  be  otherwise  perfect  at  birth, 
but  they  have  a  bluish  color  due  to  the  imper- 
fect supply  of  the  blood  with  oxygen,  and  are 
known  as  blue  babies.  The  condition  becomes 
progressively  worse  due  to  the  progressive  de- 
mands made  upon  the  heart,  and  death  takes 
place  after  some  days  or  months  or  years,  the  time 
depending  upon  the  degree  of  the  imperfection. 

Much  of  the  damage  of  the  heart  in  later  life 
is  due  to  infection.  The  valves  of  the  heart 
are  a  favorite  place  for  attack  by  certain  sorts 


224        DISEASE  AND  ITS  CAUSES 

of  bacteria  which  get  into  the  blood.  This  is 
due  to  the  prominent  position  of  the  valves 
which  brings  them  in  contact  with  all  the  blood 
in  the  body,  the  large  extent  and  unevenness 
of  the  surface  and  to  the  rubbing  together  and 
contact  of  their  edges  when  closed.  At  the  site 
of  infection  there  is  a  slight  destruction  of  tissue 
and  on  this  the  blood  clots  producing  rough 
wart-like  projections.  The  valves  in  some  cases 
are  to  a  greater  or  less  extent  destroyed,  they 
may  become  greatly  thickened  and  by  the  de- 
posit of  lime  salts  converted  into  hard,  stony 
masses.  Essentially  two  conditions  are  produced. 
In  one  the  thickened,  unyielding  valves  project 
across  the  openings  they  should  guard,  and  thus 
by  constricting  the  opening  interfere  with  the 
passage  of  blood  either  through  the  heart  or 
from  it.  In  the  other  the  valves  are  so  damaged 
that  they  cannot  properly  close  the  orifices 
they  guard,  and  on  or  after  the  contraction  of 
the  cavities  there  is  back  flow  or  regurgitation 
of  the  blood.  If,  for  instance,  the  orifice  of  the 
heart  into  the  aorta  is  narrowed,  then  the  left 
ventricle  can  only  accomplish  its  work  of  pro- 
jecting into  the  aorta  a  given  amount  of  blood 
in  a  given  time  by  contracting  with  greater 
force  and  giving  a  greater  rapidity  to  the  stream 
passing  through  the  narrow  orifice.  This  the 
heart  can  do  because,  like  all  other  organs  of  the 
body,  it  has  a  large  reserve  force  which  enables 


DISEASE  AND   ITS   CAUSES        225 

it,  even  suddenly,  to  meet  demands  double  the 
usual,  and  like  all  other  muscles  of  the  body  it 
becomes  larger  and  stronger  by  increased  work. 
The  condition  here  is  much  simpler  than  when 
the  same  valve  is  incapable  of  perfect  closure, 
or  when  both  obstruction  and  imperfect  closure, 
are  combined  as  they  not  infrequently  are.  In 
such  cases  the  ventricle  must  do  more  than  in 
the  first  case.  It  must  force  through  the  orifice, 
which  may  be  narrowed,  the  amount  of  blood 
which  is  necessary  to  keep  up  the  pressure  within 
the  aorta  and  give  to  the  circulation  the  neces- 
sary rapidity  of  flow,  and  also  the  amount  which 
flows  back  into  the  heart  through  the  imper- 
fectly acting  valve.  This  it  can  do  by  contracting 
with  greater  force  upon  a  larger  amount  of  blood, 
the  cavity  becoming  enlarged  to  receive  this. 
Not  only  may  such  damage  to  the  valves  be  pro- 
duced, but  the  muscular  tissue  of  the  heart 
may  suffer  from  defective  nutrition  or  from  the 
effect  of  poisons,  whether  these  are  formed  in 
the  body  as  the  effect  of  disease  or  introduced 
from  without ;  or  in  consequence  of  disease 
in  the  lungs  the  flow  of  blood  through  them 
may  be  impeded,  or  disease  elsewhere  in  the 
body,  as  in  the  kidneys  may,  by  increasing 
the  pressure  of  the  blood  within  the  arteries, 
throw  more  than  the  usual  amount  of  work 
upon  the  heart. 

The  power  of  the  heart  in  meeting  these  con- 


226        DISEASE  AND   ITS  CAUSES 

ditions,  however  various  they  are  and  however 
variously  they  act,  seems  little  short  of  marvel- 
lous, and  it  goes  on  throwing  three  and  one-third 
ounces  of  blood  seventy  or  eighty  times  a  minute 
into  a  tube  against  nine  feet  of  water  pressure, 
working  often  perfectly  under  conditions  which 
would  be  fatal  to  a  machine.  As  long  as  this 
goes  on  the  injury  is  said  to  be  compensated  for; 
the  increased  work  which  the  heart  is  able  to 
accomplish  by  the  exercise  of  its  reserve  force 
and  by  becoming  larger  and  stronger  enables  it 
to  cope  with  the  adverse  conditions.  With  in- 
creased demand  for  work  there  is  a  gradual 
diminution  of  the  reserve  force.  An  individual 
may  be  able  to  carry  easily  forty  pounds  up  a 
hill  and  by  exerting  all  his  force  may  carry 
eighty  pounds,  but  if  he  habitually  carries  the 
eighty  pounds,  even  though  the  muscles  become 
stronger  by  exercise  the  load  cannot  be  again 
doubled.  The  dilatation  of  the  heart  which  is 
so  important  in  compensation  is  fraught  with 
danger,  because  any  weakening  of  the  muscle 
increases  the  .dilatation,  until  a  point  is  reached 
when,  owing  to  the  dilatation  of  the  orifices  be- 
tween auricles  and  ventricles,  the  valves  become 
incompetent  to  close  them. 

When  the  heart  is  not  able  to  accomplish 
its  work,  the  eflPect  of  the  condition  becomes 
apparent  by  the  accumulation  of  blood  within 
the  veins  and  a   less  active   circulation.    This 


DISEASE  AND   ITS   CAUSES        227 

affects  the  nutrition  and  the  capacity  for  work 
of  all  the  organs  of  the  body,  and  the  im- 
perfect function  of  the  organs  may  in  a  variety 
of  ways  make  still  greater  demands  upon  an 
already  overloaded  heart.  Other  conditions 
supervene.  The  increased  pressure  within  the 
veins  and  capillaries  due  to  the  impossibility 
of  the  blood  in  the  usual  amount  passing  through 
or  from  the  heart  increases  the  amount  of  fluid 
in  the  tissues.  There  is  always  an  interchange 
between  the  blood  within  the  vessels  and  the 
fluid  outside  of  them;  the  passage  of  fluid  from, 
the  vessels  is  facilitated  by  the  increased  pressure 
within  them,  just  as  pressure  upon  a  filtering 
fluid  increases  the  rapidity  of  filtration,  and  the 
increase  of  pressure  within  veins  and  capillaries 
impedes  passage  of  tissue  fluid  into  them.  The 
fluid  accumulates  within  the  tissues  leading  to 
dropsy,  or  the  accumulation  may  take  place  in 
some  of  the  cavities  of  the  body.  The  dimin- 
ished flow  of  blood  through  the  lungs  prevents 
its  proper  oxygenation;  this  may  also  be  inter- 
fered with  by  the  accumulation  of  fluid  within  the 
air  spaces  of  the  lungs. 

Every  additional  burden  thrown  upon  the  heart 
increases  the  evil.  In  women  the  additional 
burden  of  pregnancy  may  suffice  to  overcome  a 
compensation  which  has  been  perfect,  and  the 
same  may  result  from  an  acute  attack  of  disease. 
Age,  diminishing  as  it  does  the  capacity  for  work  in 


228        DISEASE  AND   ITS  CAUSES 

all  organs,  diminishes  the  compensation  capacity 
of  the  heart,  and  a  heart  which  at  the  age  of  forty 
acts  perfectly  may  break  down  at  the  age  of  fifty. 
Compensation  may  be  gained  in  other  ways,  as 
by  reducing  the  demand  made  upon  the  heart 
by  changing  the  mode  of  life,  by  leading  an 
inactive  rather  than  an  active  life,  by  avoiding 
excitement  or  any  condition  which  entails  work 
of  the  heart.  Social  conditions  are  of  great 
importance;  it  makes  a  great  difference  whether 
the  unfortunate  possessor  of  such  a  heart  be  a 
stevedore  whose  capital  lies  in  the  strength  of 
his  muscles,  or  a  more  fortunately  placed  member 
of  society  for  whom  the  stevedore  works  and 
whose  occupation  or  lack  of  occupation  does 
not  interfere  with  the  adjustment  of  his  external 
relations  to  the  condition  of  his  heart. 

Disease  of  the  nervous  system  does  not  differ 
from  disease  elsewhere.  The  system  is  complex 
in  structure  and  in  function.  It  consists  in 
nerves  which  are  composed  of  very  fine  fibrils 
distributed  in  all  parts  of  the  body  and  serve 
the  purpose  of  conduction,  and  a  central  body 
composed  of  the  brain  and  spinal  cord  which 
is  largely  cellular  in  character;  it  receives 
impressions  by  means  of  the  nerves  and  sends 
out  impulses  which  produce  or  affect  action  in 
all  parts.  By  means  of  the  organs  of  special 
sense,  the  brain  receives  impressions  from  the 
outer  world  which  it  transforms   into  the   con- 


DISEASE  AND   ITS  CAUSES        229 

cepts  of  consciousness.  Many  of  the  impressions 
which  the  central  nervous  system  receives  from 
nerves  other  than  those  of  special  sense  and  even 
many  of  the  impressions  from  these  and  the 
impulses  which  it  sends  out  do  not  affect  con- 
sciousness. The  memory  faculty  is  seated  in 
the  brain  and  all  parts  of  the  brain  are  closely 
cormected  by  means  of  small  nerve  fibres.  The 
nervous  system  plays  an  important  part  in  the 
internal  regulation  and  coordination  of  all  parts 
of  the  body,  and  it  is  by  means  of  this  that  the 
general  adjustment  of  man  with  his  environment 
is  effected. 

Malformations  of  the  brain,  except  very  gross 
conditions  which  are  incompatible  with  extra- 
uterine existence,  are  not  very  common.  At 
birth  those  parts  of  the  brain  which  are  the 
seat  of  memory  and  what  are  understood  as  the 
higher  faculties  are  very  imperfectly  developed. 
Variations  in  structure  are  extremely  common, 
there  are  differences  in  different  individuals  in 
the  nerves  and  in  the  number,  size,  form  and 
arrangement  of  the  nerve  cells,  and  so  complex 
is  the  structure  that  considerable  variation  can 
exist  without  detection.  The  tissue  of  the 
central  nervous  system  has  a  considerable  degree 
of  resistance  to  the  action  of  bacteria,  but  is, 
however,  very  susceptible  to  injury  by  means 
of  poisons.  Serious  injury  or  destruction  of 
tissue   of   the   brain   and   spinal   cord   is   never 


230       DISEASE  AND   ITS  CAUSES 

regenerated  or  repaired,  but  adjustment  to  such 
conditions  may  be  effected  by  reciprocity  of 
function,  other  cells  taking  up  the  functions  of 
those  which  were  destroyed. 

Certain  parts  of  the  brain  are  associated  with 
definite  functions;  thus,  there  are  areas  which 
influence  or  control  speech  and  motion  of  parts 
as  the  arm  or  leg,  and  there  are  large  areas  known 
as  the  silent  areas  whose  function  we  do  not 
know.  All  activity  of  the  central  nervous  system, 
however  expressed,  is  due  to  cell  activity  and  is 
associated  with  consumption  of  cell  material 
which  is  renewed  in  periods  of  repose  and  sleep. 
Fig.  13  shows  a  nerve  cell  of  a  sparrow  at  the  end 
of  a  day's  activity  and  the  same  after  the  repose 
of  a  night. 

Diseases  of  the  nervous  system  have  a  special 
interest  in  that  they  so  often  interfere  with  man 
in  his  relations  with  his  fellows.  In  diseases  of 
other  organs  the  disturbances  set  up  concern 
the  individual  only.  Thus,  others  need  not  be 
disturbed  save  by  the  demands  made  on  their 
sympathies  by  an  individual  with  a  cold  in  the 
head  or  a  cancer  of  the  stomach.  Disease  of 
the  nervous  system  is  another  affair,  instead  of 
those  reactions  and  expressions  of  activity  to 
which  we  are  accustomed  and  to  which  society 
is  adjusted,  the  reactions  and  activities  are 
unusual  and  the  individual  in  consequence  does 
not  fit  into  the  social  state  and  is  said  to  be 


DISEASE  AND   ITS   CAUSES        231 

anti-social.  There  are  all  possible  grades  of 
this,  from  mere  unpleasantness  in  the  social 
relations  with  such  an  individual,  to  states  in 
which  he  is  dangerous  to  society  and  must  be 
isolated  from  it.  Insanity  is  an  extreme  case. 
There  is  no  disease  signified  in  the  expression, 
but  it  is  merely  a  legal  term  to  designate  those 
individuals  whose  actions  are  opposed  to  the 
social  state  and  who  are  not  responsible  for  them. 
In  insanity  there  is  falsity  in  impressions,  in 
conceptions,  in  judgment,  a  defective  power  of 
will  and  an  uncontrollable  violence  of  emotion. 
The  individual  is  prevented  from  thinking  the 
thoughts  or  feeling  the  feelings  and  doing  the 
duties  of  the  social  body  in  the  community  in 
which  he  Uves.  The  insane  are  out  of  harmony 
with  their  social  environment,  but  not  necessarily 
in  opposition  to  it. 

There  is  no  very  sharp  line  between  insanity 
and  criminality.  The  criminal  is  in  direct  an- 
tagonism to  the  laws  of  social  life.  An  insane 
person  may  cause  the  same  injury  to  society 
as  a  criminal,  but  his  actions  are  not  voluntary, 
whereas  the  criminal  is  one  who  can  control  his 
actions,  but  does  not.  Mentally  degenerated 
persons,  however,  can  be  both  insane  and  crim- 
inal. Whatever  the  state  of  society,  this  repro- 
bates the  actions  of  one  opposed  to  it;  in  a 
society  in  which  it  were  usual  to  appropriate  the 
possessions  of  others  or  to  devour  unpleasant  or 


232       DISEASE  AND   ITS  CAUSES 

useless  relatives,  virtue  and  lack  of  appetite  would 
be  reprobated  as  unsocial. 

The  symptoms  of  insanity  or  the  manner  in 
which  the  defective  action  of  the  brain  expresses 
itself  and  the  various  underlying  pathological 
changes  vary,  and  by  combining  these  it  has  been 
possible  to  subdivide  insanity  into  a  number 
of  distinct  forms.  There  are  both  intrinsic  and 
extrinsic  causes  of  insanity.  The  intrinsic  are 
the  structural  diflFerences  in  the  brain  as  com- 
pared with  the  normal  or  usual,  whether  these 
are  due  to  imperfection  in  development  or  to 
defective  heredity  or  to  the  injury  of  disease; 
the  extrinsic  causes  are  those  which  come  from 
without  and  bring  the  intrinsic  into  activity. 
Syphilis  is  a  frequent  cause  of  insanity,  and 
probably  the  only  cause  of  the  condition  known 
as  general  paralysis  of  the  insane,  acting  by 
means  of  the  injury  which  it  produces  in  the  cor- 
tex of  the  brain.  The  abuse  of  alcohol  is  another 
fertile  cause,  but  the  changes  produced  in  this 
are  not  so  obvious  as  in  the  case  of  syphilis. 
Tumors  of  the  brain  are  not  infrequently  a  cause, 
and  the  same  is  true  of  infections,  even  those 
not  located  in  the  brain.  How  susceptible  the 
brain  is  to  the  effects  of  the  toxines  of  the  in- 
fectious diseases  is  shown  in  the  frequency  of 
delirium  in  these  diseases.  There  is  an  interesting 
relation  between  this  and  alcoholism.  Alcohol 
abuse   may  produce  injury,   but  not  sufficient 


DISEASE  AND   ITS  CAUSES        233 

to  manifest  itself  under  ordinary  conditions; 
when,  however,  the  action  of  toxic  substance 
is  superadded  to  the  effect  of  the  alcohol  the 
delirium  of  fever  is   more  marked. 

Probably  of  greater  importance  than  the  ac- 
quired pathological  conditions  of  the  brain  in  pro- 
ducing insanity  is  a  congenital  condition  in  which 
the  nervous  system  is  defective.  The  most  fertile 
cause  of  insanity  lies  in  the  inheritance;  by  this  it 
must  not  be  understood  that  insane  parents  pro- 
duce insane  offsprings,  but  that  conditions  inher- 
ited from  immediate  or  remote  ancestors  appear 
in  a  diminished  resistance  of  the  nervous  system 
which  is  sooner  or  later  expressed  as  insanity. 
Given  such  a  defective  nervous  system,  extrin- 
sic conditions  which  would  have  no  effect  on 
another  individual  or  would  be  felt  in  diflFerent 
ways  may  produce  insanity.  In  these  cases 
occupation  plays  a  great  role.  The  excitement 
and  privations  of  war  especially  in  the  tropics 
and  the  ennui  of  camps  leads  to  insanity  in 
soldiers;  occupations  such  as  that  of  the  baker 
in  which  there  is  loss  of  sleep  and  the  men- 
tal strain  of  students  can  all  act  in  the  same 
way.  A  woman  who  gives  no  sign  of  nervous 
defect  may  become  insane  under  the  strain  of 
pregnancy. 

Although  insanity  is  determined  by  the  social 
relations  of  man,  that  part  of  the  social  organiza- 
tion which  is  termed  Society,  and  which  has  been 


234        DISEASE  AND   ITS  CAUSES 

developed  by  the  idle  as  a  diverting  game,  is  a 
fertile  source  of  nervous  disease  and  even  of 
insanity,  affecting  particularly  females.  The 
strenuosity  of  the  life,  the  nervous  excitement 
alternating  with  ennui,  the  lack  and  improper 
times  of  sleep,  the  lack  of  rest  and  particularly 
of  restful  occupation,  the  not  infrequent  use  of 
alcohol  in  injurious  amounts,  are  all  factors 
calculated  to  make  a  defect  operative.  The 
so-called  "coming  out"  of  young  girls  is  an 
important  element  in  the  game,  and  their  head- 
long plunge  into  such  a  life  at  a  period  under  any 
conditions  full  of  danger  to  the  nervous  system  is 
especially  to  be  reprobated.  If  we  consider 
the  influence  of  the  game  in  other  respects  as 
conducing  to  lack  of  moral  sense,  to  alcoholic 
abuse  (for  without  the  seeming  stimulation, 
but  which  is  really  the  blunting  of  impressions 
which  alcohol  brings,  the  game  would  not  be 
possible),  to  discontent,  to  mental  enfeeblement, 
it  is  all  bad.  Curiously  enough  the  game  is  one 
which  in  all  periods  has  been  played  by  the  idle, 
but  its  evil  influence  is  greater  now  than  before 
when  it  was  the  game  of  royalty  chiefly,  because 
there  are  now  more  people  living  from  the  work 
of  others. 

The  unusual  mental  action  of  the  insane  not 
infrequently  expresses  itself  by  suicide.  The 
analysis  of  three  hundred  deaths  from  suicide 
showed   pathological    changes   in   the   brain    in 


DISEASE  AND   ITS   CAUSES        235 

forty-three  per  cent,  and  when  we  think  that 
mental  disturbances  are  very  often  without 
recognizable  anatomical  changes  after  death, 
the  percentage  is  very  large.  In  another  analysis 
of  one  hundred  and  twenty-four  suicides  forty- 
four  of  these  were  mentally  affected  to  various 
degrees.  Five  of  the  men  and  seven  women  were 
epileptics,  in  ten  of  the  families  there  was  hys- 
teria, twenty-four  of  the  men  and  four  of  the 
women  were  chronic  alcoholics. 

It  is  extremely  difficult  at  the  present  time  to 
say  whether  insanity  is  increasing.  Statistics 
in  all  lands  giving  the  numbers  committed  to 
insane  hospitals  show  on  their  face  a  great  in- 
crease, but  so  many  factors  enter  into  these 
statistics  that  their  value  is  uncertain.  There 
is  now  an  ever-increasing  provision  for  the  care 
of  the  insane.  Owing  to  the  recognition  of 
insanity  as  a  part  of  nervous  disease  and  its 
separation  from  criminality  there  is  no  longer 
the  same  attempt  to  conceal  it  as  was  formerly 
the  case,  and  hospitals  for  the  insane  are  no  longer 
associated  with  ideas  of  Bedlam.  It  is  generally 
believed  that  modern  conditions  in  the  hurry 
and  excitement  of  life,  and  the  extreme  social 
differences,  the  greater  urban  life,  the  greater 
extension  of  factory  life,  all  tend  to  an  increase 
in  insanity,  but  there  is  no  absolute  proof  that 
this  is  true.  We  know  very  little  about  insanity 
in  the  Middle  Ages,  but  the  conditions  then  were 


236       DISEASE  AND   ITS  CAUSES 

not  conducive  to  a  quiet  life.  There  prevailed 
then  as  now  excess  and  want,  luxury  and  poverty, 
enjoyment  and  deprivations,  balls  and  dinner  par- 
ties and  other  features  of  the  social  game.  There 
were  factions  in  the  cities,  public  executions,  not 
infrequent  sieges,  scenes  of  horror,  epidemics, 
famines,  and  all  these  combined  with  religious 
superstition  and  the  often  unjust  and  cruel  laws 
should  have  been  factors  for  insanity.  There 
were  actual  epidemics  of  insanity  affecting  masses 
of  the  population,  as  shown  in  the  children's  cru- 
sade, the  Jewish  massacres  and  the  dancing 
mania  in  the  Rhine  provinces.  WTiere  civilization 
seems  to  be  the  highest,  statistics  show  the 
most  insane,  but  this  most  probably  depends  up- 
on better  recognition  of  the  condition  and 
better  provision  for  asylum  care. 

The  so-called  functional  diseases  have  a  close 
relation  with  diseases  of  the  nervous  system,  for 
they  chiefly  concern  the  reactions  of  nerve  tissue. 
Disease  expressing  itself  in  disturbance  of  function 
only,  does  not  seem  to  fit  in  with  the  conceptions 
of  disease  which  have  been  expressed,  nor  can 
we  imagine  a  disturbance  of  function  which 
does  not  depend  upon  a  change  of  material. 
Living  matter  does  not  differ  intrinsically  from 
any  other  sort  of  matter;  like  other  matter  its 
reactions  depend  upon  its  composition  structure^ 

*  By  structure  as  used  in  this  wide  sense,  there  must  be 
understood  not  merely  the  anatomical  structure,  which  is 


DISEASE  AND   ITS  CAUSES        237 

and  the  character  of  the  action  exerted  upon  it. 
By  functional  disease  there  is  expressed  merely 
that  no  anatomical  or  chemical  change  is  discover- 
able in  the  material  which  gives  the  unusual  reac- 
tion. The  further  our  researches  into  the  nature  of 
disease  extend,  particularly  the  researches  into 
the  physiology  and  chemistry  of  disease,  the 
smaller  is  the  area  of  functional  disease.  In 
functional  disease  there  may  be  either  vague 
discomfort  or  actual  pain  under  conditions 
when  usually  such  would  not  be  experienced, 
and  on  examination  no  condition  is  found  which 
in  the  vast  majority  of  cases  would  alone  give 
rise  to  that  impression  on  the  nervous  system 
which  is  interpreted  as  pain.  In  the  production 
of  the  sensations  of  disease  there  can  be  change 
at  any  place  along  the  line,  in  the  sense  organs, 
in  the  conducting  paths  or  in  the  central  organ. 
Thus  there  may  be  false  visual  impressions 
which  may  be  due  to  changes  in  the  retina  or 
in  the  optic  nerve  or  in  the  brain  matter  to 
which  the  nerve  is  distributed.  It  is  perfectly 
possible  that  substances  of  an  unusual  character 
or  an  excess  or  deficiency  of  usual  substances  in 
the  fluids  around  brain  cells  may  so  change  them 
that  such  unusual  reactions  appear.  There  may 
be,  of  course,  very  marked  individual  susceptibil- 

revealed  by  the  dissecting  knife  and  microscope,  but  molecu- 
lar structure,  or  the  manner  in  which  elements  are  arranged 
to  form  the  molecule,  as  well. 


238        DISEASE  AND   ITS  CAUSES 

ity,  which  may  be  congenital  or  acquired.  The 
perception  of  every  stimulus  involves  acti\aty  of 
the  nerve  cells,  and  it  is  possible  that  the  constant 
repetition  of  stimuli  of  an  ordinary  character  may 
produce  sufficient  change  to  give  rise  to  unusual 
reactions,  and  this  particularly  when  there  is 
lack  of  the  restoration  which  repose  and  sleep 
bring.  We  know  into  what  a  condition  one's 
nervous  system  may  be  thrown  by  the  incessant 
noise  attending  the  erection  of  a  building  in  the 
vicinity  of  one's  house  or  the  pounding  of  a 
plumber  working  within  the  house,  this  being 
accentuated  in  the  latter  case  by  the  thought 
of  impending  financial  disaster.  Even  the  con- 
fused and  disagreeable  sound  due  to  the  clatter 
of  high-pitched  women's  voices  at  teas  and 
receptions  may,  when  frequently  repeated,  be 
productive  of  changes  in  the  nerve  cells  suffi- 
ciently marked,  to  give  rise  to  the  unusual  reac- 
tions which  are  evidence  of  disease. 

In  the  condition  known  as  neurasthenia,  which 
is  often  taken  as  a  type  of  a  functional  disease, 
the  basal  and  intrinsic  cause  is  activity  of  the 
nervous  system  with  the  using  up  of  material 
which  is  not  compensated  for  by  the  renewal 
which  comes  in  repose  and  sleep.  Neurasthenia 
is  one  of  the  common  conditions  of  our  civili- 
zation, found  among  children  and  adults,  the 
poor  and  rich,  the  idle  and  the  factory  worker; 
it  is  rife  in  the  scholastic  professions  and  among 


DISEASE  AND   ITS  CAUSES        239 

those  who  earn  their  living  by  brain  work.  It 
seems  to  be  more  common  in  the  upper  classes 
and  particularly  in  the  women,  but  this  is  because 
these  are  more  subject  to  medical  care  and  the 
condition  is  more  in  evidence.  There  are  all 
sorts  of  symptoms  attached  to  the  condition, 
for  the  unusual  mental  action  can  be  variously 
expressed.  The  cerebral  form  has  been  thus  de- 
scribed by  a  well-known  medical  writer:  "One  of 
the  most  characteristic  features  of  cerebral  neuras- 
thenia is  a  weary  brain.  The  sensation  is  familiar 
enough  to  any  fagged  man,  especially  if  he  fall 
short  of  sleep.  Impressions  seem  to  go  half  into 
one's  head  and  there  sink  into  a  woolly  bed  and 
die.  Voices  sound  far  off,  the  lines  of  a  book 
run  into  one  another  and  the  meaning  of  them 
passes  unperceived.  Doors  bang  and  windows 
rattle  as  they  never  did  before;  if  a  shoestring 
breaks,  an  imprecation  is  upon  the  lips.  Business 
matters  are  in  a  conspiracy  to  go  wrong.  Letters 
are  left  unopened  partly  from  want  of  will, 
partly  from  a  senseless  dread  lest  they  contain 
bad  news.  At  night  the  patient  tosses  on  his  bed 
possessed  by  all  the  cares  which  blacken  with 
darkness.  Headache  is  common,  loss  of  memory 
is  distressing,  and  in  severe  cases  it  is  wider  and 
deeper  than  mere  inattention  can  explain.  There 
is  often  the  torture  of  acute  hearing,  or  an  in- 
ability to  suppress  attention;  the  hater  of  clocks 
and    crowing    cocks    is    a    neurasthenic."      The 


240       DISEASE  AND   ITS  CAUSES 

disease  is  especially  common  in  the  women 
players  of  the  social  game,  and  its  unhappy 
victims  too  often  seek  relief  from  the  nervous 
irritability  which  is  a  common  early  symptom 
in  still  greater  nervous  excitement.  It  is  a  sad 
commentary  on  our  civilization  that  one  of  the 
means  of  treatment  for  these  persons  which  has 
been  found  eflBcacious  is  to  supply  them  with  some 
restful  household  occupation  such  as  knitting 
or  plain  sewing,  and  there  are  institutions  which 
combine  refuge  from  social  activities,  often  called 
duties,  with  simple  occupation. 


CHAPTER  XII 

The  Rapid  Development  of  Medicine  in  the  Last  Fiitt 
Years.  —  The  Influence  of  Darwin.  —  Preventive 
Medicine.  —  The  Dissemination  of  Medical  Knowl- 
edge.—  The  Development  ok  Conditions  in  Recent 
Years  which  Act  as  Factors  of  Disease.  —  Factory 
Life.  —  Urban  Life. — The  Increase  of  Communica- 
tion BETWEEN  Peoples.  —  The  Introduction  of  Plant 
Parasites. — The  Increase  in  Asylum  Life.  —  Infant 
Mortality.  —  Wealth  and  Poverty  as  Factors  in 
Disease. 

Certain  conditions  have  arisen  in  the  past 
fifty  years  which  have  profoundly  affected  the 
thoughts,  the  beliefs  and  the  activities  of  man. 
Within  this  period  what  is  generally  known  as 
Darwinism,  including  under  this  evolution,  has 
developed.  Unlike  theories  which  came  from 
philosophical  speculation  only,  the  theory  of 
evolution  was  one  which  could  be  subjected  to 
observation  and  experiment.  It  freed  man's  mind 
from  dogmas,  it  stimulated  the  imagination,  it 
enlarged  the  territory  in  which  it  seemed  possible 
to  extend  knowledge  by  the  methods  of  science, 
and  has  resulted  in  an  enormous  increase  of 
knowledge.  This  has  been  more  striking  in  medi- 
cal science  than  elsewhere,  and  in  this  of  more 
far-reaching  influence.  Evolution  coincided  with 
another  important  development.  History  shows 
241 


242       DISEASE  AND  ITS  CAUSES 

that  all  great  periods  of  civilization  have  at 
their  back  sources  of  energy.  In  the  civilizations 
of  the  past  such  sources  of  energy  have  come 
from  the  enslavement  of  conquered  peoples  or 
from  commerce,  or  more  direct  forms  of  robbery, 
which  have  enabled  a  favored  class  to  appropri- 
ate for  its  purposes  the  results  of  the  work  of 
others.  While  these  sources  have  not  been 
absent  in  the  development  of  our  civilization, 
the  great  source  of  energy  has  come  from  the 
rapid,  and  usually  wasteful  and  reckless,  utiliza- 
tion of  the  stored  energy  of  the  earth.  The 
almost  incredible  advance  in  medical  and  other 
forms  of  scientific  knowledge  and  the  utilization 
of  this  knowledge  is  largely  due  to  the  greater 
forces  which  we  have  become  possessed  of. 

Disease  plays  such  a  large  part  in  the  life  of 
man  and  is  so  closely  related  to  all  of  his  activ- 
ities that  the  changes  in  this  period  must  have 
exerted  an  influence  on  disease.  We  have  already 
seen  that  within  the  period  we  have  obtained 
knowledge  of  the  causes  of  disease  and  the  con- 
ditions under  which  these  causes  became  oper- 
ative. The  mystery  which  formerly  enveloped 
disease  is  gone;  disease  is  recognized  as  due  to 
conditions  which  for  the  most  part  are  within 
the  control  of  man,  and  like  gra\dty  and  chemical 
attraction  it  follows  the  operation  of  definite 
laws.  There  has  been  developed  within  the 
period  what  is-  known  as  preventive  medicine, 


DISEASE  AND   ITS  CAUSES        243 

which  aims  rather  at  prevention  than  cure,  and 
the  resources  of  prevention  are  capable  of  much 
greater  extension. 

Have  there  been  new  conditions  developed 
within  the  period,  or  an  increase  of  existing 
conditions  which  can  be  regarded  as  disease  fac- 
tors and  which  counterbalance  the  results  which 
have  come  from  the  knowledge  of  prevention 
and  cure?  There  has  been  an  increase  of  certain 
factors  of  immense  importance  in  the  extension 
of  disease.     These  are: 

1.  The  increase  in  industrialism,  involving  as 
this  does  an  increase  in  factory  life.  In  many 
ways  this  is  a  factor  in  disease,  (a)  By  favoring 
the  extension  of  infection,  particularly  in  such 
diseases  as  tuberculosis.  (6)  The  life  indoors,  and 
frequently  with  the  combination  of  insufficient  air 
and  space,  produces  a  condition  of  malnutrition 
and  deficient  general  resistance,  (c)  The  family  life 
is  interfered  with  by  the  mothers,  whose  primary 
duty  is  the  care  of  home  and  children,  working  in 
factories,  and  the  too  frequent  conversion  of  the 
house  into  a  factory,  (d)  The  influence  of  factory 
life  is  towards  a  loss  of  moral  stamina  rendering 
more  easy  of  operation  the  conditions  of  alco- 
holism and  general  immorality.  How  great  has 
been  this  increase  in  industrialism,  fostered  as 
it  has  been  by  conditions  both  natural  and  arti- 
ficially created  by  unwise  legislation,  is  shown 
in  the  figures  from  the  last  census.    The  number 


244        DISEASE  AND   ITS  CAUSES 

of  factory  operatives  increased  forty  per  cent 
between  1899  and  1909  and  the  total  population 
of  the  country  in  the  period  between  1900  and 
1910  increased  twenty  per  cent.  It  is  probable 
that  the  future  will  see  an  extension  rather  than 
a  diminution  of  mass  labor. 

2.  The  increase  in  urban  life  is  as  conspicuous 
as  the  increase  in  industrialism.  In  1880,  twenty- 
nine  and  five-tenths  per  cent  of  the  population 
was  urban  and  seventy  and  five-tenths  per  cent 
was  rural;  in  1910,  forty -six  and  three-tenths  per 
cent  was  urban  and  fifty -three  and  seven-tenths 
was  rural,  the  increase  being  most  marked  in  cities 
of  over  five  hundred  thousand  inhabitants.  Of  the 
total  increase  in  population  between  1900  and  1910, 
seven-tenths  per  cent  was  in  the  cities  and  three- 
tenths  per  cent  in  the  country.  City  life  in  itself  is 
not  necessarily  unhealthy  and  there  are  many 
advantages  associated  with  it.  The  conditions 
which  have  chiefly  fostered  it  are  the  immigration 
of  people  who  are  accustomed  to  community 
life,  the  increase  in  factory  life  and  the  increased 
number  of  people  of  wealth  who  seek  the  advan- 
tages which  the  city  gives  them.  The  city  has 
always  been  the  favored  playground  for  the 
social  game.  The  unhealthy  conditions  of  city 
life  are  due  to  the  crowding,  the  more  uncertain 
means  of  livelihood,  the  greater  influence  of  vice 
and  alcoholism.  Prostitution  and  the  sexual 
diseases  are  almost  the  prerogatives  of  the  cities. 


DISEASE  AND   ITS   CAUSES        245 

3.  All  means  of  transportation  have  increased 
and  communication  between  peoples  has  become 
more  extended  and  more  rapid.  In  the  past 
isolation  w  as  one  of  the  safeguards  of  the  people 
against  disease.  With  the  increase  and  greater 
rapidity  of  communication  there  is  a  tendency 
not  only  to  loss  of  individuality  in  nations  as 
expressed  in  dress,  customs,  traditions  and  be- 
liefs, but  many  diseases  are  no  longer  so  strictly 
local  as  formerly  —  pellagra,  for  example.  Only 
those  diseases  which  are  transmitted  by  insects 
which  have  a  strictly  local  habitat  remain  endemic, 
although  the  region  of  endemic  prevalence  may 
become  greatly  extended,  as  is  seen  in  the  dis- 
tribution of  sleeping  sickness.  Diseases  of  plants 
and  of  animals  have  become  disseminated.  Any 
plants  desirable  for  economic  use  or  for  beauty 
of  foliage  and  flower  become  generally  distributed, 
their  parasites  are  removed  from  the  regions  where 
harmonious  parasitic  inter-relations  have  been 
established,  and  in  new  regions  the  parasites 
may  not  find  the  former  restrictions  to  their 
growth.  There  have  been  many  examples  of 
this,  such  as  the  ravages  of  the  brown-tail  and 
gypsy  moths  which  were  introduced  into  New 
England  and  of  the  San  Jose  scale  which  was 
introduced  into  California.  There  have  been 
many  other  examples  of  the  almost  incredible 
power  of  multiplication  of  an  animal  or  plant 
when  taken  into  a  new  environment,  removed 


246       DISEASE  AND   ITS  CAUSES 

from  conditions  which  held  it  in  check,  as 
the  introduction  of  the  mongoose  into  Jamaica, 
the  rabbit  into  Australia,  the  thistle  into  New 
South  Wales  and  the  water-plant  chara  into 
England. 

It  is  very  difficult  to  say,  but  it  seems  as  though 
there  is  an  increasing  unevenness  in  the  distribu- 
tion of  wealth,  an  increase  in  the  munber  of 
persons  who  live  at  the  expense  of  the  laboring 
class.  Mass  labor,  effective  though  it  be,  makes 
it  easier  to  divert  the  proceeds  of  labor  from  the 
laborers.  The  evidence  of  this  is  seen  in  the  in- 
crease in  number  and  the  prosperity  of  those  pur- 
suits which  purvey  to  luxury,  as  the  automobile 
industry  and  the  florists'  trade  and  the  greatly 
increased  scope  and  activity  of  the  social  game. 
On  the  other  hand,  there  is  an  increase  in  the 
number  of  people  who  are  to  a  greater  or  less 
extent  dependent  upon  extraneous  aid,  evinced 
among  other  ways  by  the  increase  in  the  asy- 
lum populations.  Both  these  conditions,  wealth 
and  poverty,  are  important  disease  factors. 
Tuberculosis  is  now  a  disease  of  the  proletariat 
chiefly.  The  measures  both  of  prevention  and 
cure  can  be  and  are  carried  out  by  the  well-to-do, 
but  the  disease  must  remain  where  there  are  the 
conditions  of  the  slums.  Of  all  the  conditions 
favoring  infant  mortality  poverty  comes  first. 
In  Erfurt,  a  small  city  of  Germany,  of  one  thou- 
sand infants  bom  in  each  of  the  different  classes, 


DISEASE  AND   ITS  CAUSES        247 

there  died  of  the  illegitimate  children  three  hun- 
dren  and  fifty-two;  of  those  of  the  laboring 
class,  three  hundred  and  five;  of  those  in  the 
medium  station  (oflScial  class  largely),  one  hun- 
dred and  seventy-three;  of  those  in  higher 
station,  eighty-nine.  The  same  relation  of  infant 
mortality  to  poverty  becomes  apparent  when 
estimated  in  other  ways.  In  Beriin,  with  an 
average  infant  mortality  of  one  hundred  and 
ninety-six  per  thousand,  the  deaths  in  the  best 
districts  of  the  city  were  fifty-two  and  in  the 
poorer  quarters  four  hundred  and  twenty.  The 
effect  of  poverty  is  seen  particularly  in  the  bottle- 
fed  infants;  with  natural  nursing  the  child  of 
poverty  has  almost  as  good  a  chance  as  the 
child  of  wealth.  From  reasons  which  are  almost 
self-evident,  the  mortality  in  illegitimate  infants 
is  almost  double  that  of  the  legitimate.  The 
greater  infant  mortality  in  poverty  is  due  to 
the  more  numerous  children  preventing  indi- 
vidual care,  the  separation  of  the  mother  from 
the  nursing  child  in  consequence  of  the  demand 
made  upon  her  earning  capacity,  and  the  decline 
in  breast  nursing.  Wealth  is  on  the  whole  more 
advantageous  from  the  narrow  point  of  view  of 
disease  than  is  poverty,  but  if  we  regard  its 
influence  on  the  race  its  advantages  are  not  so 
evident.  Nothing  can  be  worse  for  a  race  than 
that  it  should  die  out,  and  wealthy  families  have 
never  reproduced  themselves.    Conditions  always 


248       DISEASE  AND   ITS  CAUSES 

tending  to  destruction  are  a  necessary  part  of 
the  environment  of  poverty;  wealth  voluntarily 
creates  these  conditions,  and  chiefly  by  the  per- 
nicious influence  of  its  amusements  on  the  young. 
A  new  and  in  many  respects  a  nobler  concep- 
tion of  medicine  has  been  developed.  Formerly 
medical  practice  was  almost  exclusively  a  per- 
sonal service  to  the  sick  individual,  and  measures 
looking  toward  the  general  relief  of  disease  and 
its  prevention  received  scanty  consideration. 
The  idea  of  a  wider  service  to  the  city,  to  the 
state,  to  the  nation,  to  humanity  rather  than 
the  personal  service  to  the  individual,  is  becoming 
dominant  in  medicine.  This  is  seen  in  the  estab- 
lishment of  laboratories  by  boards  of  health  in 
cities  and  states  in  which  knowledge  obtained  by 
exact  investigations  can  be  made  of  direct  service 
to  the  people;  in  the  medical  inspection  of  schools 
and  factories;  in  promulgating  laws  directed 
against  conditions  which  affect  health,  in  the 
extension  of  hospitals,  and  in  divers  other  ways. 
The  idea  of  public  service  and  of  returning  to 
the  people  in  an  effective  way  some  of  the  results 
of  their  labor  also  underlies  the  large  donations 
which  have  been  given  for  the  creation  of  special 
laboratories  and  institutes  in  which,  through 
research,  greater  knowledge  of  disease  may  be 
obtained  and  made  available.  The  researches 
which  have  been  made  on  the  nutrition  of  man 
and  the  nutritive  value  of  different  foods  are  of 


DISEASE  AND   ITS  CAUSES         249 

great  importance,  and  this  knowledge  has  not 
yet  begun  to  be  appHed  as  it  should  be. 

There  seems  to  be  a  balance  maintained  be- 
tween the  restriction  of  disease  by  prevention 
and  the  increased  influence  of  social  conditions 
which  are  in  themselves  factors  of  disease. 
Preventive  medicine  seems  to  have  made  pos- 
sible, by  restricting  their  harmful  influence,  the 
increase  in  industrialism,  in  urban  life,  and  in 
the  intercommunications  of  peoples.  The  most 
important  aid  in  the  future  to  the  influence  of 
preventive  medicine  must  be  the  education  of 
the  people  so  that  the  conditions  of  disease,  the 
intrinsic  and  the  extrinsic  causes  and  the  manner 
in  which  these  act,  shall  all  become  a  part  of 
general  knowledge,  and  the  sympathy  of  the 
people  with  health  legislation  and  their  active 
assistance  in  carrying  out  measures  of  preven- 
tion may  be  obtained.  The  effect  of  social  con- 
ditions on  disease  must  become  more  generally 
recognized. 


GLOSSARY 


Atrophy  —  A  condition  of  imperfect  nutrition  producing 
diminution  in  size  and  loss  of  function  of  parts. 

Bertillon  —  A  French  anthropologist  who  devised  a 
system  of  measurements  of  the  human  body  for  purposes  of 
identification. 

Blood-plasma  —  The  fluid  of  the  blood. 

Cell  —  The  unit  of  living  matter.  Living  things  may  be 
unicellular  or  composed  of  a  multitude  of  cells  which  are  inter- 
dependent. The  general  mass  of  material  forming  the  cell  is 
termed  cytoplasm.  In  this  there  is  a  differentiated  area 
termed  nucleus  which  governs  the  multiplication  of  cells.  In 
the  nucleus  is  a  material  termed  chromatin  which  bears  the 
factors  of  heredity. 

Chemotropism  —  The  influence  of  chemical  substances  in 
directing  the  movement  of  organisms. 

Exudate  —  The  material  which  passes  from  the  blood  into 
an  injured  part  and  causes  the  swelling. 

Fibrin  —  The  gelatinous  material  formed  in  the  blood 
when  it  clots. 

Hemoglobin  —  A  substance  which  gives  the  red  color  to 
the  blood;  by  means  of  its  ready  combination  with  the  oxygen 
of  the  air  in  the  lungs  this  necessary  element  is  carried  to  all 
parts  of  the  body. 

Inflammation  —  Literally  a  "burning";  the  changes  which 
take  place  in  a  part  after  injury. 

Lymph  —  The  fluid  which  is  contained  in  the  lymphatic 
vessels  —  nodes.  Circumscribed  masses  of  cells  connected 
with  the  lymphatic  vessels. 

Osmosis  —  The  process  of  diffusion  between  fluids  of  dif- 
ferent molecular  pressures. 

Spore  Formation  — A  mode  of  reproduction  in  lower  forms 
of  life  by  which  resistant  btxlies,  spores,  are  formed.  These 
have  many  analogies  with  the  seed  of  higher  plants. 

Symbiosis  —  A  mutual  adaptation  between  parasite  and 
host. 

Transudation  —  The  normal  interchange  of  fluid  between 
250 


GLOSSARY  251 

the  blood  and  the  tissue  fluids.  The  material  interchanged 
is  the  transudate. 

Tkopism  —  The  influence  of  forces  which  direct  the  move- 
ment of  cells. 

Ultra-microscope  —  A  form  of  microscope  which  by  means 
of  oblique  illumination  renders  visible  objects  so  small  as  to 
be  invisible  with  the  ordinary  microscope. 

Vraus  —  A  substance  either  living  or  formed  by  living 
things  which  may  cause  disease. 


INDEX 


Amoeba,  13 
Anthrax,  109 
Antitoxin,  154 

Bacteria,  116 

adaptation  in,  123 

aerobic,  122 

anaerobic,  122 

artificial  cultivation  of,  119 

distribution  in  nature,  121 

growth  and  reproduction, 
118 

mode  of  action  in  disease, 
144 

size,  117 

spore  formation,  118 

substances  affecting  growth 
of,  123 

toxin  production  by,  144 

variations  in,  123 
Blood,  35 

circulation  of,  33,  80 

vessels,  32 
Body,  22 

defenses  of,  146 

organs  of,  28 

reserve  force  of,  50 

surfaces  of,  22 
Brain,  31 


Cerebro-spinal       meningitis, 

188 
Chemotropism,  93 
Cretinism,  37 

Darwinism,  240 
Death,  57 

decomposition  after,  51 
rigor  after,  60 
signs  of,  59 
Disease,  1 

action  of  poisons,  44 
acute  and  chronic,  219 
industrialism  as  factor  in, 

243 
lesions  of,  46 

superstitions  concerning, 
10 
urban  life  as  factor  in,  244 
wealth  and  poverty  as  fac- 
tors in,  246 
Ductless  glands,  37 

Embryo,  77 
Epilepsy,  209 
Eugenics,  215 

Foetus,  32 

infection  of,  200 
Foot  and  Mouth  Disease,  129 


252 


INDEX 


253 


Glands,  22 
Growth,  62 

Heart,  33,  221 

disease  of,  223 
Heliotropism,  93 
Heredity,  197 

influence  of  alcohol,  206 

of  insanity,  209 

variations  and  imitations, 
204 
Hookworm  disease,  179 

Immunity,  148 

theories  of,  149 

natural,  150 
Infection,  135 

from      external       surface, 
136 

from    genito-urinary    sur- 
face, 137 

from  lungs,  138 

from  mouth,  138 

from   stomach   and   intes- 
tines, 139 

from  wounds,  141 

in  children,  195 

in  wild  animals,  191 

latent,  166 

mixed,  160 

racial      susceptibility     to, 
191 

resistance  to,  143 

by  air,  170 

by  insects,  171 


Infectious  diseases,  97 

carriers  of,  185 

comparison  with  fermenta- 
tion, 108 

epidemics  of,  98 

endemic,      epidemic      and 
sporadic  forms,  188 

modes  of  transmission,  161 
Inflammation,  80 

acute  and  chronic,  95 
Injury,  54-74 
Insanity,  231 

causes  of,  232 

question  of  increase,  235 

Lesion,  17 
Leucocytes,  36 

migration  of,  92 
Living  matter,  10 

Malaria,  175 
role  of  mosquito  in  trans- 
mitting, 178 

Malformations,  211 
heredity  of,  215 

Maternal  impressions,  212 

Nervous  system,  228 

disease  of,  230 

effect  of  social  life  on,  233 
Neurasthenia,  238 

Old  age,  51 
atrophy  in,  51 
blood  vessels  in,  54 


254 


INDEX 


Old  age  —  continued. 
causes  of  death  in,  56 
in  animals  and  plants,  55 
mental  activity  in,  53 

Osmosis,  91 

Opsonins,  153 

Oviun,  201 

fertilization  of,  198 
infection  of,  199 

Phagocytosis,  86 

Plague,  182 

transmission    by    animals, 
183 

Plasmodium  Malariae,  175 

Preventive  medicine,  242 

Protozoa,  124 

distribution  in  nature,  125 
mode  of  growth,  125 
sexual  differentiation,  li25 
spore  formation,  125 

Polyomyelitis,  190 

Repair,  46 
conditions  influencing,  47 

Scar.  49 

Skin,  21 

Sleeping  sickness,  173 

Smallpox,  187 

Spontaneous  generation,  106 


Sunb.um,  83 
Syphilis,  193 

Tetanus,  142 
Thymus,  52 
Thyroid,  37 
Tonsils,  52 
Toxins,  144 
Tropisms,  93 
Trypanosomes,  172 
Tuberculosis,  163 

infection  by  sputum,  169 

modes  of  extension,  163 
Tumors,  64 

benign  and  malignant,  69 

cells  of,  66 

color,  size  and  shape,  65 

growth  of,  65 

importance  of,  77 

origin  of,  66 

question  of  increase,  69 

theories  of  cause,  71 

treatment  of,  77 
Typhoid  fever,  170 

Ultra-microscopic  organisms, 
128 

Virus,  128 

Yellow  fever,  178 


UNIVERSITY  OF  CAUIFORNIA  AT  LOS  ANGELES 
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DEC  U  RBTD 

JAM  5    1950 

NOV  3  0^950 

JAN  3     195!| 
MAY  16  19M 

MOV  4 -195ft 

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